Thread:Project:Support desk/Special:Upload - Argument 2 is not an array/reply

All variables are defined in DefaultSettings.php. In LocalSettings.php you override them when applicable. If you don't have them in LocalSettings.php, they'll have the default value

I guess somewhere in your code you have $wgFileBlacklist set to null. Try to grep the code to see if you can find where $wgFileBlacklist is set to null.

Maybe it's some of your extensions. Try disabling them.