.Net 4.0 AccessViolationException

Hi, I'm having a problem with windows and a third party device library. We develop software that uses third party hardware, written for .Net 4.0+ in C# for both 32/64 bit platforms according to target computer. In this case it's a Windows 7 64bit computer.

I installed our software in the user's computer (a big company with lots of System/Network/User settings and restrictions) and all worked fine and we were able to use it perfectly. After a reboot, the computer's user privileges (apparently) changed and now the application crashes on startup. Looking through the Event Viewer, the error is caused by an Access Violation Exception, which is not CLR so it cannot be caught on .Net versions above 2.0.

The error itself is caused when trying to scan for connected devices, and the weird part is, our software will crash but the device manufacturer's software will detect the device correctly. I've already contacted the manufacturer's dev team and so far we couldn't find any reason for this, which sounds about right since this looks more like a permissions problem, not a device driver problem.

I have uninstalled, cleaned and reinstalled everything I could think of, asked for higher user privileges (admin level), tried "Run as Admin" on every possible configuration and nothing seems to work! I always get the same error.

In short, I installed, it worked, something changed and I could never get it to work again! Is there anything I can check or clean or change to fix this?

Thank you very much!