Windows Backup Logon Failure

I did recently Install a server with windows 2012 for BACKUPS. 

When Im trying to schedule a backup of my webserver trougth the network sharing to the BACKUP -Server, at the final step I get an error message saying Logon Failure: Username wrong or password bad data. 

What should I do? Do I need to add some credential on my Backup server?

The username and the Password that Im typing is the Administrator-account from the backup-server. 

Opening trougth the file explorer works fine:
\\169.254.29.86\c$\Backup\WINDOWS-Y8IEYWB

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