Thread:Project:Support desk/Update previous MW 1.16.5 to 1.17.0 throws an 500 internal server error/reply (7)

The preprocessor is probably one of the more memory-hungrey parts of MediaWiki if you're rendering a very complex page (I assume anyways). Also check your LocalSettings.php file. Some really older versions of MediaWiki had a line setting the memory limit to something way too low. (However, MediaWiki 1.17 will automatically try to raise the memory limit to 50 mb if it detects if its lower than that).

You could also try adding a line like  to the bottom of LocalSettings.php, but MediaWiki already does something similar, so it probably wouldn't work.