Cannot create a shadow copy of the volumes containing writer's data. A VSS critical writer has failed. Writer name: [SqlServerWriter]

We recently faced backup failure for Application aware backup in Veeam for MSSQL server. The error is listed below,

Processing <VM_Name> Error: Unfreeze error: [Backup job failed. Cannot create a shadow copy of the volumes containing writer's data.

A VSS critical writer has failed. Writer name: [SqlServerWriter]. Class ID: [{a65faa63-5ea8-4ebc-9dbd-a0c4db26912a}].

Instance ID: [{41239125-29f6-4455-9bc1-32439ceebe75}]. Writer's state: [VSS_WS_FAILED_AT_PREPARE_SNAPSHOT]. Error code: [0x800423f0].]

Normally this is caused by NTDS writers issue and we can easily fix it by restating the below services,

before restarting, I listed 'vssadmin list writers' through cmd, I found that, writer was in failed state

Writer name: 'SqlServerWriter'

Writer Id: {a65faa63-5ea8-4ebc-9dbd-a0c4db26912a}

Writer Instance Id: {41239125-29f6-4455-9bc1-32439ceebe75}

State: [8] Failed

Last error: Inconsistent shadow copy

So I have restarted the below services and ran above cmd  again and no error found.

COM+ Event System

Volume Shadow Copy

MSSQL VSS services.

Here backup will success after the retry.

Today, I got same error and I tried same fix, however got same error and it was surprise to me.

I checked the Log for the Veeam backup in MSSQL  server and found the below error,

                Connecting to mssql, connection string: Provider='msoledbsql';Data Source='Server_Name';Integrated Security='SSPI';Persist Security Info=False, timeout: 15

                Instance '' connection problem: Code = 0x80040e4d

         Code meaning = IDispatch error #3149

           Source = Microsoft OLE DB Driver for SQL Server

             Description = Login failed for user 'user_Name'.

We found that there were some new MSSQL instance created in this server and the service account was not added for those instance to access and backup.

Finally we provided permission to same account to newly created instances and issue got fixed.