I have just moved my mediawiki 1.15 installation over to a new server and upgraded to the 1.24 version.
PHP version 5.6.0; MySQL version 5.6.21
The upgrade seemed to go smoothly, with some expected problems. I had to remove StartProfiler.php; I had to remove old skins; I removed the out-of-date extension FCKEditor; the AutomaticRemoteUser extension does not seem to be working. I can worry about the extensions later, though.
Right now I can view and edit pages OK, which is why I say the upgrade seems to have gone fine.
However, none of my Special pages work! They all give an error similar to:
Fatal error: Call to undefined method SpecialSpecialpages::setContext() in E:\www\wiki\includes\specialpage\SpecialPageFactory.php on line 553
UPDATE: I fixed it. The error was caused by an old GoogleMaps extension that was deprecated. I thought it was commented out but it wasn't!
Thanks!