DLL file not found when invoking function from Excel/VBA

Question

DLL file not found when invoking function from Excel/VBA

Chris Grossman 25

I'm running Windows 11 with 64-bit MS/Office 2021. I have a very large (>25KSLOC) Excel/VBA application with a helper DLL written in C and compiled by Visual Studio 2022. The last time I used the app was May 4, 2025, and it worked perfectly. Today, June 28, it won't run. When it gets to the first invocation of a DLL function, it gets the all-too-familiar "File Not Found" VBA error message. But nothing has changed since May 4. The DLL file is unchanged and is in exactly the same place it's always been, and its only dependency (a known cause of the File Not Found error) is Kernel32.dll, which my W11 system most definitely has. And the exact same glitch occurs on my W10 box running 32-bit Excel 2016: ran fine 2 months ago and now crashes with 'File Not Found'. Any ideas how I can determine what's causing the error today when it wasn't happening 2 months ago? I have noticed there have been a couple large Windows Updates over the last 2 months, on both W11 and W10 boxes. Hopefully Microsoft didn't change something that is now making my code fail.

Viorel 123.6K Reputation points

2025-06-29T15:14:54.9766667+00:00

Maybe you should recompile the DLLs (using latest Visual Studio), building corresponding files for 64- and 32-bit Excel.

You can also conduct more complicated investigations, trying to analyze the problem using a new simplest DLL, or to check if new workbooks can access some simple library functions, such as Declare PtrSafe Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long).
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Guido Bartel 0 Reputation points

2025-07-09T15:00:22.0966667+00:00

I have the same problem. Suddenly my DLL functions in VBA are not working any longer. Always error message "file not found". Even if i set Drive/Dir to the directory where the DLL is located. Only solution for me was to hardcode the complete path in the LIB Parameter of the Declare Statement. I don't know what happend to my environment.

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Your answer

Viorel 123.6K Reputation points

2025-06-29T15:14:54.9766667+00:00

Maybe you should recompile the DLLs (using latest Visual Studio), building corresponding files for 64- and 32-bit Excel.

You can also conduct more complicated investigations, trying to analyze the problem using a new simplest DLL, or to check if new workbooks can access some simple library functions, such as Declare PtrSafe Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long).
Deleted

This comment has been deleted due to a violation of our Code of Conduct. The comment was manually reported or identified through automated detection before action was taken. Please refer to our Code of Conduct for more information.
Guido Bartel 0 Reputation points

2025-07-09T15:00:22.0966667+00:00

I have the same problem. Suddenly my DLL functions in VBA are not working any longer. Always error message "file not found". Even if i set Drive/Dir to the directory where the DLL is located. Only solution for me was to hardcode the complete path in the LIB Parameter of the Declare Statement. I don't know what happend to my environment.

Answer 1

Chris Grossman 25

This problem was solved by Ryan, a Microsoft Community Support Specialist, on another thread. Microsoft changed the way VBA can reference a DLL so it no longer uses the current directory. The solution I ended up using was to have the VBA code invoke the SetDefaultDllDirectories and AddDllDirectory Windows API functions. I can provide the specific code snippet if desired.

Carlos Moreno 0 Reputation points

2025-07-11T15:52:30.7933333+00:00

Hi Chris, greetings from Mexico, I'm having exactly the same problem, I think, I'm declaring 2 dlls, 1 works by adding the full path, other doesn't as has embedded DLLs, I think I need to implement the solution you mention.

Can you provide the snippet of your code as you offered?

Thank you in advance.

Carlos M.
Geoff Riggs 0 Reputation points

2025-07-29T01:05:53.7233333+00:00

Hi Chris, I am having the same issue, could you provide the code snippet you refer to or direct to the thread where it is resolved? Many thanks, Geoff
Chris Grossman 25 Reputation points

2025-08-01T19:32:40.8733333+00:00

Here is the code that I ended up using:

Public Const DLL_SEARCH_DEFAULT_DIRS As Long = &H1000

Declare PtrSafe Function AddDllDirectory Lib "kernel32" _

(ByVal lpPathName As LongPtr) As LongPtr

Declare PtrSafe Function SetDefaultDllDirectories _

Lib "kernel32" (ByVal DirectoryFlags As Long) As Long

Dim pRC As LongPtr

' Tell Windows to use all paths in the DLL search

Call SetDefaultDllDirectories(DLL_SEARCH_DEFAULT_DIRS)

' Add MyLib to the set of DLL paths

pRC = AddDllDirectory(StrPtr(sLibPath))

...add error checking here...

The code works on both Windows 11 w/Office 2021 and Windows 10 w/Office 2016.

Hope this helps.

-Chris
Riggs, Geoff 0 Reputation points

2025-08-05T19:49:37.0733333+00:00

Thanks Chris: I'll have to do a bit of tweaking, but that gives me a better sense of your approach. - Geoff
Jon Petter Grandal 0 Reputation points

2025-08-07T15:11:01.1666667+00:00

Thank you Chris! I have the exact same problem.

A user reported that my DLL call (Public Declare Sub PILSSExcelAPI Lib "PILSS_DLL.dll") worked before the summer, but not after the summer. I managed to replicate the error on a VM (Windows 11). Excel version 16.0.18623.20208 works with no problems. Excel version 16.0.19029.20136 throws error 53 even if I hardcode the full path to the dll. I guess a temporary work-around would be to downgrade the Excel version.

Do you have the link to the thread where you mentioned "Ryan, a Microsoft Community Support Specialist" had solved the problem?

I btw. quickly tried you VBA code, but no luck. I might have to tweak it some to fit my code.
Chris Grossman 25 Reputation points

2025-08-08T15:26:49.3433333+00:00

Jon, the new "feature", as I understand it, has nothing to do with Excel version or Windows version (occurs on Excel 2016/Windows 10 just as it does on Excel 2021/Windows 11). It was a security update to the Windows kernel that was pushed to both Windows 10 and 11 in April. I tried backing out the Windows update with no luck (Windows Update says that some changes cannot be backed out). I can't find the link to the other thread right now, but I'll keep looking for it. I suggest you keep trying to tweak the code example I posted. Like I said, it worked for me. The one thing I would add that might not be obvious from the code snippet, the 'sLibPath' variable is just a simple String field that contains the path to the folder containing the DLL file, e.g., "D:\MyStuff\MyDLLFolder". Hope this helps. Good luck!
Jon Petter Grandal 0 Reputation points

2025-08-13T09:07:41.64+00:00
Thanks again Chris!

I've done some further testing on VMs and pinpointed which Excel versions causes problems. I'll share my findings for reference for other who experience this issue. Although, I'm not sure it helps, other than that a temporary work-around can be to rollback the Excel version. I've not yet tried to tweak your code further.

Summary:

I've tested on Windows 11 and with various versions of Microsoft Excel for Microsoft 365 MSO 32-bit with the Windows version frozen.

Excel Version 2504 (Build 18730.20186) and older loads the DLL normally (as Excel has since at least 2016/2017 when my workbook was created).

With Excel Version Version 2505 (Build 18827.20128) and newer, the DLL is not found (VBA error 53).

I've mass tested on Windows 11 24H2 26100.3775, which includes KB5055523 and KB5054979 that were installed on April 23rd, 2025. I don't know if any of these Windows updates include the troublesome security update to the Windows kernel that you mention.

I've also tested that the same behaviour (Excel Version 2504 Build 18730.20186 still works) prevails on newer Windows versions:

Windows 11 24H2 26100.4652

Windows 11 24H2 26100.4946

Also tested that the "culprit" Excel Version Version 2505 (Build 18827.20128) fails on older Windows version I uninstalled the two "April packages":

Windows 11 24H2 26100.2894

Further info:

Note, for this mass testing, I've only tested the workbook as is, meaning that VBA first change CurDir to where the DLL is located, then loads it from the current directory.

I've simply tested the Excel versions one by one by following this guide: https://support.microsoft.com/en-us/topic/how-to-revert-to-an-earlier-version-of-office-2bd5c457-a917-d57e-35a1-f709e3dda841

Only tested "Current Channel" versions.

Specific Excel builds tested on Windows 11 24H2 26100.3775 (plus some spot checks on other Win11 versions):

OK: Version 2503 (Build 18623.20208), Version 2504 (Build 18730.20122), Version 2504 (Build 18730.20186)

Fail: Version 2505 (Build 18827.20128), Version 2505 (Build 18827.20140), Version 2505 (Build 18827.20176), Version 2507 (Build 19029.20136), Version 2507 (Build 19029.20156)

Strange observation regarding Excel versions:

Excel can state that it's of two different build at once. This happens for the 2505 family and also 2507. Example:

Go to Excel -> File -> Account -> About Excel: Version 2505 (Build 18827.20128)

Go to Excel -> File -> Account -> About Excel -> About Excel button: Version 2505 (Build 18827.20102)

This 18827.20102 build is particularly strange as I can find traces of it in cached google searches, but not on any official Microsoft Excel/Office release notes. It is also a build that Excel can't find if you specify to install this version. Yet, all the 2505 builds claim to be build 18827.20102 when you click the About Excel button. Weird.

I haven't found any rationale for why this happens. It's probably as you say, but appears to be included in a security update for Excel in isolation as well. It could maybe be related to this security update for Excel, but that's just my guessing: https://support.microsoft.com/en-gb/topic/description-of-the-security-update-for-excel-2016-may-13-2025-kb5002717-ee01b6a2-8257-4650-84fc-dcfd6f120c0e

Answer 2

simo-k 57,980 Volunteer Moderator

Please check whether the DLL library reference settings are properly configured on the VBA side.

Chris Grossman 25 Reputation points

2025-06-29T15:07:41.8733333+00:00

simo-k,

Thanks for responding. I don't know what you mean by 'DLL library reference settings'. In VBA, the function is declared thus:

Declare PtrSafe Function ProcInit Lib "M64.dll" (arg1 As MGD_Com) As Long

and the invocation is coded as:

Sim_Init_CE = ProcInit(MC)

I have confirmed that the current drive/path is pointing to the folder containing 'M64.dll' just before the invocation. And, like I said in the original post, this code has been working successfully for years, and just this week started failing.-Chris Grossman
simo-k 57,980 Reputation points Volunteer Moderator

2025-06-29T15:34:07.0866667+00:00

This is a screen capture in Japanese, and the area framed in red is the part.

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DLL file not found when invoking function from Excel/VBA

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