Thread:Project:Support desk/Upgrading from 1.18 to 1.22.1 stuck at Upgrade existing installation

I have updated all the files via FTP and am now attempting to run the web updater (I've entered the upgrade key etc).

The upgrade seems to be stuck at the "Upgrade existing installation" stage and I can't get passed it. It throws no errors except "There are MediaWiki tables in this database. To upgrade them to MediaWiki 1.22.1, click Continue." It thinks for a bit when clicking "continue" but then...nothing.

Just above the "Backtrace" information in the window, it shows:

I've added the php error debug code to the top of the localsettings.php and the page reports:

Help?