XAMPP error when I try to run my localhost page

I have been encountering this problem when i try to my localhost host page on my browser. I'm using firefox as my browser. Before it works fine but a on the later day this error suddenly appear.
Any solution for this?
Warning: include() [function.include]: Failed opening 'lang/' for inclusion (include_path='.;C:xamppphpPEAR') in C:xampphtdocsxamppindex.php on line 12
