Backup cannot save a snapshot of the volumes on this computer because the computer does not have enough storage space available. ...

Backup cannot save a snapshot of the volumes on this computer because the computer does not have enough storage space available. 

To resolve this issue, either add more storage space to this computer, or free up some space on an existing drive. 

For information about how to resolve issues with Backup, see the Troubleshooting section in the online Help