Compared to developing shaders on ATI cards, the nVidia development is starting to drive me nuts. The error messages are some of the most unhelpful that could be devised. The worst bit that I've been finding is that in one run of the application I'll get no errors, in the next, with no changes in code, I'll get a collection of errors. Googling for the exact phrases doesn't return any results.
I'd appreciate some suggestions on nVidia-specific forums to peruse. Ideally, some pointers to a complete documentation of the shader implementation would make life much simpler.
For example, here is one message that I sometimes get during the program link (the compilation step produces no errors):
Code :Vertex info ----------- Internal error: assembly compile error for vertex shader at offset 0: -- error message -- line 1, column 1: error: invalid vertex program header -- internal assembly text --