It might be the data base corruption issue. Try to recreate the database like described here
1. Go to Control panel > Administrative Tools and run Services. Stop the Veeam Endpoint Backup service.
2. Run regedit.exe and locate the HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Endpoint Backup key. Create the following value under this key:
Name = Recreatedatabase
Type = DWORD
Value = 1
3. Start Veeam Endpoint Backup service
4. Allow some time for the new database instance to be created (5 minutes should be enough).
5. Stop Veeam Endpoint Backup service
6. Run regedit.exe and delete the Recreatedatabase value from HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Endpoint Backup key.