For the general C++ project/solution setup:
1. Errors or warnings beginning with a 'C' are compiler errors or warnings.
2. Errors or warnings beginning with a 'L' are linker errors or warnings.
3. Header files are mostly needed by the compiler (ressouce compiler, too - special case)
4. Library and object files (.lib .obj) are used by the Linker.
5. Visual Studio (C++) Projects have nearly all the properties you need to change at the project (.vcxproj)
So when a header is not found, you immediately know:
a) it's a
compiler setting you have to check
b) it's in a project setting (Right click on project in "Solution Explorer" Tree - select "Properties")
c) as it's a
compiler setting, you have to take a look at the
C++ section ("C++" -> "General" -> "Additional Include Directories" in this case).
There you should have at least have one entry pointing to
Orbitersdk\include.
Usually this is done by using a makro (
$(SDKIncludeDir) for Orbiter projects)
Getting Linker errors, you can proceed with a similar reasoning:
a) it's a linker setting you have to check
b) it's in a project setting (Right click on project in "Solution Explorer" Tree - select "Properties")
c) as it's a linker setting, you have to take a look at the Linker section ("Linker" -> "General" -> "Additional Library Directories" for a .lib not found example).
There you should have at least have one entry pointing to
Orbitersdk\lib.
Usually this is done by using a makro (
$(SDKLibDir) for Orbiter projects)
...
The second part is just a general description to show the steps one has to think through to get to a result and is
not specific to this issue 
