I upgraded my version to 1.5.20. I ran the update.php and everything showed ok. Then when I clicked the link to versioncheck I got a white page with Fatal Error. So I went to the main index page and also got Fatal Error. What should I do?
Enable debug in your database >> Config. using a tool like Phpmyadmin.
That could help to show a more detailed error message.
Leftover cpg 1.4.x plugins could also cause trouble.
If you have a bridged gallery you might have to unbridge.
Go to bridgemgr.php in your site.
Take a look at the Upgrade instructions to see if you have missed anything.
http://documentation.coppermine-gallery.net/en/upgrading.htm
If you still have trouble and are able to enable debug mode, post a link to your Coppermine.