Thread:Project:Support desk/Web Updater Error/reply

Are you sure you have replaced all the old files with the new ones?

If I remember correctly there was the advise to install MediaWiki 1.18.x into a new directory. That means you should not just take the new files and override the old files with them, but really make sure that no old core files are left. Create a new directory and unpack the new source code there. Then move the content of your extensions/, images/ and skins/ folder and your LocalSettings.php there as well and then try running the Web Updater.