VS6- C++ Error executing cl.exe

The following error occurs when running a c++ program that works. It works on the hundreds of other workstations that I support, but for one.

c:\program files\microsoft visual studio\vc98\include\errno.h(29) : fatal error C1021: invalid preprocessor command 'extern'
Error executing cl.exe.

 

That looks like a compile-time error, certainly not a runtime error unless I'm missing something here. So why not compile it on one of the other machines and then just copy the .exe?