The issue is resolved now. djensen has informed me, that he freed up some space.
I have already tested it, and new savegames will be uploaded to the forum correctly as well as downloaded to the user’s harddrive.
The forum software doesn’t allow to purge by specific file type and date range. It’s one-by-one or a date range only. I’ll blast away all files older than one year old but I guess there are none right now.