Thread:Project:Support desk/Mediawiki internal error: Another module has already been registered as oojs (ResourceLoader.php)/reply

I don't know of the exact internals, but this error means that the OOjs module has tried to be registered multiple times. I would guess that this can happen, if you use old extensions or an old skin, which are not properly updated for MediaWiki 1.24. Maybe you still have files from the old MediaWiki version in the way, which are now causing trouble. In this case updating them should solve the issue.

In order to investigate, which extension might cause this, you might try disabling all extensions and then enabling them one by one until you get the error again!