I had just completed a PHP5 upgrade on my development server and I got this error.
I had already enabled long arrays so that wasn't the problem.
The system output the entire contents of coppermine.inc.php then spit out this error.
Fatal error: Call to a member function authenticate() on a non-object in c:\Inetpub\wwwroot\devel\include\init.inc.php on line 263
I found that coppermine.inc.php didn't have a "php" in it's starting processor directive.
<?
/*************************
Coppermine Photo Gallery
************************
changing to
<?php
/*************************
Coppermine Photo Gallery
************************
Solved the problem.
fix committed.