Daily backups failing with "A backup to the same destination is already running"

Hello there,

Sorry, I don't mean to cross post - I posed a comment on source forge, but then realized it might a different issue.

My nightly backups are failing with the message: "A backup to the same destination is already running with PID 5919". This is the same error message with the same PID I got the night before (making this failure #2)

So I kill 5919, but the question are:

1) should I worry that the backup process will fail again? 2) how do I find out why the backup process got stuck for 48 hours?

The destination FTP server is valid and successfully used on another virtualmin server. I have made no modifications to the backup job and the FTP server in 6 months..

My virtualmin version is 3.82

Thank you for any help