Error:
CExBackup::backupService:HrESEBackupSetup: Error Number 0x50d: (null)
Cause:
The message suggests that the Exchange VSS writer has detected that an earlier Exchange snapshot backup operation is in an unfinished state. Therefore, the current backup operation and all subsequent backup operations are unsuccessful.
Resolution:
If an earlier Exchange snapshot backup operation is in progress, wait for the backup operation to finish before you start the next Exchange snapshot backup operation.