Windows 10 Backup mystery

I've recently been dragged, kicking and screaming, into Windows10. I have set up my backup to go to a network drive (NAS). Unfortunately the backup has failed with the attached cryptic message. Since I have no virtual disks I don't understand the message. When I look at the event viewer it is of little help. I've attached the general tab (not copiable) and here is the detail tab:

- System
- Provider
[ Name] Microsoft-Windows-Backup
[ Guid] {1db28f2e-8f80-4027-8c5a-a11f7f10f62d}
EventID 517
Version 1
Level 2
Task 0
Opcode 0
Keywords 0x8000000000000000
- TimeCreated
[ SystemTime] 2022-04-10T07:12:09.4155432Z
EventRecordID 2246
Correlation
- Execution
[ ProcessID] 600
[ ThreadID] 10344
Channel Application
Computer dap001
- Security
[ UserID] S-1-5-18
- EventData
BackupTime 2022-04-10T07:00:14.2218663Z
ErrorCode 0x807800c5
ErrorMessage %%2155348165


Can someone help me fix this? TIA.

 

I googled a lot of stuff but not that specific error number. I guess the bottom line is to use a 3rd party backup solution.