A virtual comport suddenly stopped working. Device manager shows the comport but it can't be accessed. What could be the cause?

Hi Minjon,

Since everything was working fine yesterday, it’s reasonable to suspect that a recent Windows update or system change may be causing the issue.

Here are a few steps you can try to help narrow down the root cause:

Go to Settings > Windows Update > Update History and check whether any USB, chipset, or cumulative updates were recently installed.

Open Device Manager, expand Ports (COM & LPT), and see if any COM ports show warnings or errors. If they do, try uninstalling the affected USB converter device and then reconnect it to let Windows reinstall the driver.

If you suspect a specific driver update, try rolling it back: Right-click the device > Properties > Driver > Roll Back Driver

If available, try connecting the USB converter to another system that hasn’t received recent Windows updates. This can help confirm whether the issue is update-related.

Let me know how it goes!

Hi Beatrix, thanks for getting back to me. In the meantime, I've done some further research and discovered that using a terminal program to communicate directly with a COM port worked fine. However, all of our programs that couldn't connect to our peripherals use configuration files with COM port settings. These configuration files are modified by their respective programs. When I checked these configuration files, they weren't the most recent versions. OneDrive had overwritten them with older versions and repeated this process as soon as their respective programs updated them.

Disabling OneDrive solved the problem for now. The next step is to resolve the OneDrive sync issue, but that's another story.

Anyway, thanks for your adequate suggestions.

Hi Beatrix, thanks for getting back to me. In the meantime, I've done some further research and discovered that using a terminal program to communicate directly with a COM port worked fine. However, all of our programs that couldn't connect to our peripherals use configuration files with COM port settings. These configuration files are modified by their respective programs. When I checked these configuration files, they weren't the most recent versions. OneDrive had overwritten them with older versions and repeated this process as soon as their respective programs updated them.

Disabling OneDrive solved the problem for now. The next step is to resolve the OneDrive sync issue, but that's another story.

Anyway, thanks for your adequate suggestions.