Thread:Project:Support desk/MediaWiki 1.21 internal error

I just updated 5 wikis, all on the same webspace, to version 1.21. All the updates were successful, and 4 of the 5 wikis run without any problem. One of them gives me the error "MediaWiki 1.21 requires at least PHP version 5.3.2, you are using PHP 5.2.17." This is very odd, because the others work, and according to my service provider (1and1.com) the wikis are using PHP 5.4. The upgrade process recognized that the wiki is using PHP 5.4.20. and completed the entire process successfully.

What would cause this to happen? This wiki dates back to 2007, but it was previously upgraded and running fine under version 1.17 or so (I'm not exactly sure of the version, but that is what I remember.) What do I do to get this running? The wiki is here. Thanks in advance for any advice offered.