Thread:Project:Support desk/Unable to upgrade MediaWiki/reply

What does it mean with "custom header"? Sure, you can set header data with PHP, but why does that influence their update script? All I can say is that this error message does not come from MediaWiki.

If you also have Shell- or FTP-access to the server, you should be able to do the update without using this buggy installer by following the instructions on Upgrading.