>>------------------------
>>So, could it be that I need to specify (for now) the whole path to that dll? The dll is included into the project (not as a reference) and I checked Always copy as you suggested in another message.
>
>The error:
>
>A first chance exception of type 'System.DllNotFoundException' occurred in Siriusware.Middleware.dll
>
>Seems to suggest that yes, it's not finding your DLL (well, it's not finding SOME DLL, not sure which). Yes, embed the full path (prefix with @"C:\PathToDll\").

Here is the new error I got:

------ Run test started ------
An exception occurred while invoking executor 'executor://mstestadapter/v1': Object reference not set to an instance of an object.
========== Run test finished: 0 run (0:03:28.8149436) ==========

I guess I need to send this info to the developer of this dll. May be some properties need to be initialized properly. In case of VFP we're using ini file with ODBC and DB settings. In C# we're using connection string. May be this is what's causing the problem.