Failed to pre-process the job Error: Sequence contains more than one element 

We have run into issues where backups fail with the following message:

Failed to pre-process the job Error: Sequence contains more than one element

These seem to be related to disconnections to the backup storage or the repository storage filling up while the backups are running.

There are a few different ways we have found to resolve these issues:

1. If you have recently upgraded to Veeam v12 and your backup copies are still “Legacy Backup Copy” jobs, you can upgrade the backup chain. Typically, the next time the job runs after the upgrade it will run successfully. These are the steps for that process:
   1. First disable the backup copy job getting the error.
   2. Next create a new backup copy job. You will notice that some of the options for the new backup copy job are different than the “Legacy Backup Copy” job settings.
   3. On the Target tab, select the original backup repository, then click on the Map Backup option.
   4. Select the original backup. You will get a warning about upgrading the backup chain.
   5. Make sure that you are using an XFS or ReFS backed Veeam Repository, otherwise the upgrade process will create a new full backup file and double your backup storage. Mind the warning about the original backup files following background retention rules.
   6. Finish configuring the backup copy job and an upgrade window will pop up.
   7. Wait for the upgrade to finish, then enable the job and run it.
2. Re-map the backup files to the job:
   1.  From the Veeam console, under Backups, right click on the backup files and remove from configuration.
   2. Go to Backup Infrastructure and rescan the destination repository. The removed backup should be re-added to the Backups menu.
   3. Edit the backup copy job and go to the Target tab then click on the Map Backup option under the repository drop down.
   4. Select the re-added backup file and click Next through the remaining pages and finish.
   5. Re-run the job.
3. Open a Veeam support case. In some cases, Veeam support can provide additional options to fix this error.
4. As a last resort you can also clone the backup copy job and run it to create a new active full backup.