Theres a very strange thing that the C18 compiler does....
How many characters is the path to your project files? There is a limit to the number of characters allowed.
I would suggest trying copying all of your files to a directory near the root, in my case, i use: "C:\firstcode\<year>\<day/revision>"
Did that work? Post back here or PM either way. Hope that helps you, if you need other help i'm not a 1/2 bad programmer.
-Q