I have encountered this warning on Veeam Backup & Replication version 18.104.22.168 on one Exchange Server 2007 VM.
The issue started the backup wants to run, but Veeam was unable to freeze the guest machine to take hot backup, and the snapshot left inside the datastore of the VM and Veeam didn’t remove it. Veeam job was configured to re-try the failed job after 15 minuets. Again, when it’s started, the Veeam created a snapshot and when it failed, Veeam didn’t remove the snapshot. This issue has caused the datastore to be filled up and left without space :)
Manually, I consolidated all the snapshots and deleted all of them. Then when I started the VM, luckily started fine.
But, when I re-run the Veeam Job, it started but very slow and gives the following warning. Cannot use CBT: Soap fault. Error caused by file.
Edit the Veeam Backup Job, and in the Virtual Machines section, hit the button Recalculate. This will recalculate the exchange disks and will be re-added veeam/vCenter database. After that, the job started as incremental without warning and full backup without warning and faster :)