Thread:Project:Support desk/Upgrade from 1.16 = 1.21 failure/reply (3)

Part of the problem might be that you have overwritten the old files. This leaves other files, which are no longer there in the new release, in place. This can cause problems.

Instead of overwriting files, try putting your install in a new folder. Manual:Upgrading and especially the section "command line" contain some hints on which files to keep.