[SOLVED] Veeam Endpoint Backup: 28.11.2016 16:20:44 :: Creating VSS snapshot Error: Failed to create snapshot: Backup job failed. Cannot create a shadow copy of the volumes containing writer's data. VSS asynchronous operation is not completed.

Problem & Context:

You're using the great Veeam endpoint backup (https://www.veeam.com/free-backup) but suddenly backups stop working and you encounter the following error message:
"Creating VSS snapshot Error: Failed to create snapshot: Backup job failed. Cannot create a shadow copy of the volumes containing writer's data. VSS asynchronous operation is not completed. Operation: [Shadow copies commit]. Code: [0x8004230f]."
+
"Error: Failed to create snapshot: Backup job failed. Cannot create a shadow copy of the volumes containing writer's data. VSS asynchronous operation is not completed. Operation: [Shadow copies commit]. Code: [0x8004230f]."

Solution:

https://www.veeam.com/kb1794

For me the problem was that the shadowstorage size was too low for some partitions. So I set it to 20% for each partition, restarted and it's working! :)

vssadmin resize shadowstorage /for=C: /on=C: /maxsize=20%
vssadmin resize shadowstorage /for=D: /on=D: /maxsize=20%