Customized ''Simple Invoices'' will not work on lampp.

Help needed to get a PHP script to work on a Lampp server. I have had a customization of "Simple Invoices" made. It runs fine on the programmers server, but when I install it on my Ubuntu Linux maschine's Lampp server, it comes up with a require_once error. I have checked permissions, filepath structure and [login to view URL] setup. But nothing have worked. The original "Simple Invoices" works just fine on the server. The error come up for all the files in the following folder: modules/customers/tabs/ These are the files added by the programmer. I do not know which other files have been corrected so the files in the tab folder works. I use the newest Lampp setup on the newest Ubuntu 8.04. ## Deliverables It is very important that the script can run on Lampp using Ubuntu 8.04.