There is already a thread marked solved for this issue https://www.3cx.com/community/threads/backup-failure.47438/page-2 I have same problem on two 3CX installations. Unchecking call history on the backup makes it work. Though it is not a problem for me to purge the call history in one of the 3CX that experiment this problem there is no way I can do it on another client PBX. Don't know how to purge call history anyway. So I'm now with a 3CX which last backup is on 30 August 2017. Both are 3CX v15.5 upgraded from v15 and upgraded from v14. The backups some time ago where very very large and I found a huge folder with phone templates which is not present on v15 so I deleted it on both systems. But I don't think this is related to the problem as the backups continued working for a long time after that. I think the problem is on call history backup because when it is disabled the manual backup works correctly. The log in verbose mode says nothing at all about the backup process so I can't figure out nothing about the issue. This issue most probable was introduced on one of the last 3CX updates as both 3CX started showing this problem on 30 August. Fresh 3CX v15 install does not show this problem. Any clue of what's happening? I would need to solve this without losing data.