[Richard McClellan]

I had that same problem about a month ago. It has to do with MPLab not recognizing the compiler. I was getting the message because I installed MPLab after the C18 compiler, and you really need to do it in the other order.

There might be a way to fix it by changing something in your build options or something, but I don't know what exactly, so I uninstalled the C18 compiler, and reinstall it, and it worked.