Program stops after some time

We have made a multithreaded server/client program. It works fine, but after some time it stops with a messagebox that says "Setup error Failed to load resources please check your setup" Why can't .NET show a normal error-message?

This error is very difficult to debug, since it happens after days of normal use of the application. Anyone have tips on how to debug such errors?

I did a search for you, but seems this issue is not well addressed. Some say that 'You probably make reference to an other assembly that it has not been copied '.