While I don't like posting stuff from other web logs I found an interesting post to reinforce my distrust of multiple languages in .Net.
The example is using C# classes and just calling it from C# and VB.Net.
The difference in results is explained because overloading behaviour is not standard. It's up to the compiler of the language. So VB.Net find the "closests" method in the class hierachy. C# uses the direct parents class (as I would think).
You can produce enough bugs using one language, forget about trying to figure out the problems caused by cross language integration.