If you have validated the SCP/FTP credentials then I would suggest upgrade to 8.1.2. There were some issues with Extreme Management Center being able to complete script processes for backups that have been fixed.
If the issue still exists in 8.1.2 I would suggest creating a case with GTAC.
Have you validated that you have set SCP and FTP credentials in XMC?
In XMC (Oneview) Administration>Options>Inventory Manager>File Transfer>FTP Transfer properties
and SCP Transfer Properties- Login Information
Make sure you input your login credentials for EMC