Here is a support article with that error. Does that apply?
Perhaps the debugger is eating an excaption the VE3D API is throwing. In VS, do a ctrl+alt+e and change it to break whenever any exception is thrown. This can be tedius b/c it will break on all your try catch blocks, but it might give you some information.
Here is some info. about that PlugInLoader. It seems to imply it must be called from the FirstFrameRendered eventhandler. Perhaps one of your forms is doing that and one not?