Re: Warning: Class '…' not found in …
From semantic-mediawiki.org
Fragment of a discussion from Help talk:Installation
To wrap up, I just did a successful SMW upgrade on MediaWiki 1.22, without any outstanding issues though "Initialise or upgrade tables" may not succeed in one go (memory issues most likely). I need to revert now to SMW 1.8.0.5 as SF is not yet compatible with this release, but I'm hopeful that everything will work out.