If the migration caused a large buildup of transaction logs, this was expected and the server has plenty of space to accomodate them. What we were not expecting was the amount of time a backup would take. DPM 2010 has been running a replica creation for about 6 hours now, We are assuming this is because we have around 100,000 1MB log files which should be purged after the backup is complete.
We can solve this problem by turning off ESEUTIL on DPM2010 and running a backup.
This allowed the backup to complete as it was ESEUTIL causing timeouts (due to the massive number of transaction logs)
Once this initial backup was complete DPM purged the transaction logs, We then turned ESEUTIL back on and ran a normal backup.