Went into check on the status of the backups (like a good sysadmin) and get the attached error when going through the webadmin
I also was going to do a tidy (all our backups get moved to tape) so ran
[zimbra@mail ~]$ zmbackup -del 7d
Error occurred: system failure: unable to retrieve latest session-account, account name-id maps
I've done a stop and start of the service using zmcontrol and everything seems to be running fine, just no backups.