Sounds like maybe there is insufficient disk space in the guest to perform the indexing? Try increasing the disk capacity or freeing up enough space to have 1-2 GB of free space on each drive.

@haslund Thank you for your suggestion, but I have about  2.61 TB   free space on the disc that I used for storage, I think the disc space might not be problem.
 

Sorry I was unclear, I didn’t mean the backup repository but rather the virtual disks of the virtual machine you are backing up.

Do the logs tell you any more?  Located here - C:\ProgramData\Veeam\Backup

@haslund Thank you much for yor reply againn, Yes it looks like the problem is here in VM disks. I have thre vHDD and one of that is corrupted and cannot be accesses. that might cause problem, I will fix this and check again. Thanks
@Chris.Childerhose you are right,  I will also check if I found log, now cannot locate in both C:\Program Files\Veeam   & 
C:\Program Files (x86)\Veeam

@haslund Thank you much for yor reply againn, Yes it looks like the problem is here in VM disks. I have thre vHDD and one of that is corrupted and cannot be accesses. that might cause problem, I will fix this and check again. Thanks
@Chris.Childerhose you are right,  I will also check if I found log, now cannot locate in both C:\Program Files\Veeam   & 
C:\Program Files (x86)\Veeam

 

Definitely that E drive could possibly cause the issue with the backup throwing the message.  Hopefully that fixes it for you.

Kind reminder to mark an answer as the best answer if your question has been resolved. If not, could you update us what the current status is?

@haslund thanks for reminding me that, I did it now, and  it was best answer :)