>>My only guess is that the SqlCommand.CommandText is empty - but you say it's not so........
>
>No, it does contain correct information - I see it in the debug window (and I expanded parameters as well to verify).
>
>I got suggestion to try IntelliTrace but I think it doesn't apply for my version of Visual Studio (Premium).

With David Browne's help from MSDN thread on this topic I finally got to the root of the problem. Somehow the wrong DB was used instead of the one I am supposed to be using. Now I just need to figure out where that connection is set in the Windows Form app (as in Tests project it is correct).