Thread:Project:Support desk/Web updater for upgrade 1.19 1.22 blacks out

Upgrading from MW 1.19.7 to 1.22 fails as the web updater proceeds straightaway from the initial page to the dreaded blank page (the URL shown is "[...]/mw-config/?page=ExistingWiki"). I've already commented out most of the extensions except ConfirmEdit, SimpleSecurity and Renameuser, and the memory limit has been set to a generous 2000+ M. Without an error message of some kind (even if error reporting is on) it is difficult to tell where to start. Any idea how diagnose this or better yet, how to solve this?