ParserFunctions installation issue - Windows / IIS7
You need to ensure the filecache has been enabled:
$wgUseFileCache = true; /* default: false */ $wgFileCacheDirectory = "$IP/cache"; $wgShowIPinHeader = false;
Note (for other onlookers) - This is unrelated to ParserFunctions - Basically $wgFileCacheDirectory has to point to the right place for the i18n cache to work (Assuming storing i18n cache in files is enabled. I do not believe it is by default) . The error probably occurred when installing parser functions as that causes all existing caches to be cleared.