Unresolved externals occur when linker cannot find the memory mapping of a function/variable that is called in the program.
To correct your error include glut32.lib in your project settings. It mapps the memory address of the function to the one in the glut32.dll so that the linker can find it there.
There sometimes is a problem when you are using incompatible versions of dll, lib and /or header files. Make sure all are consistent (i.e. belong to the same version)