No error message is seen.
This happens when the email address of a recently deleted mailbox is added as an alias on the affected mailbox in Office 365. The O365 sync will disable the Veritas Alta Archiving account configured with this alias.
Either remove the deleted mailbox's email address as an alias on the affected Veritas Alta Archiving account, or force delete the deleted address from the Recycle Bin of Office 365.
List of all the deleted users can be found by connecting to the MsolService via PowerShell and running the below cmdlet.
Get-MsolUser -ReturnDeletedUsers
Once the deleted user, which has been added to an active mailbox is identified, the below cmdlet can be used to permanently delete it.
Remove-MsolUser -UserPrincipalName johndoe@democloud.com -RemoveFromRecycleBin
After permanently deleting the user, a Clean Sync should be initiated using the Veritas Office 365 Sync to enable the incorrectly disabled archive.