What kind of backup job @ozgurarm ?? Regular? Tape? 

Regular

What kind of Repository are you backing up to? Is this a new backup or has it been running awhile? What version of Veeam are you using?

Check out the job log located at: C:\ProgramData\Veeam\Backup\<job-name>.log to see if there is any more details about the error.

Also, have you investigated any network disconnects to the repository?

When asking for help more details are needed, however, remember this is not a technical support forum either so we can only offer advice.

Veeam version?

Type of job?

More error details from logs as screenshot does not help?

Is the firewall ports open or is it off causing blocking?

Have you added antivirus exclusions if using an AV product?

This can also be database related. Are you using SQL Instance?

Secondly this can also be an issue if the write protection is enabled on the physical tape. If you have access to the physical tape you can try toggling the on and off button.

@ozgurarm Make sure write protection is off on that tape by going to Media Pool

Right click on the tape and you should see protect option. Make sure its unchecked.

I've been dealing with this problem for 4 days. It was fixed by deleting past snapshots. What I don't understand is, there was already space on the disk, why did this happen?

Hi @ozgurarm -

Glad you were able to solve the issue you were having. So others may benefit who have the same issue, we ask you to mark your last comment as ‘Best Answer’. 

As far as “why this happened”...well, as we are not Tech Support, your best bet, if you’re still wanting to investigate cause, is to contact Veeam Technical Support. 

If you have further questions, don’t hesitate to ask.

Thank you.