Can't see header

I'm using MSVC++ 6.0 and I have created a class. The declaration is in a .hpp file and the implementation is in a .cpp file. Both files have been manually added to the project and the .hpp file is included in the main file. Yet it won't build as it says my class is not a class or namespace. The compiler can clearly find the header file (because it's not saying it can't) but still the class declaration cannot be seen by the compiler.

I'm tearing my hair out - as far as I'm aware I've done everything necessary and it just refuses to build.

Show us some code (stripped down if necessary but something that still demonstrates the same error you are getting). Also include the exact error messages that are displayed.