Hey, I am having the same problem, but on the web interface I don't have the option to purge or delete files, so I keep getting the no space error. Are you able to just delete everything that is on my online backup so I can start over. I have also been on the Phone to support people but they just said to buy more storage, which i did get another 5GB but still i have no space. LOL
<<edit: subject edited for the moved post to reflect the issue>>
Before we proceed with an engineering level purge - have you gone to File Actions and then Purge Files to remove content directly? You can also remove the computer, which will uninstall Norton Online Backup and purge that computer, to start fresh. It's also important to note the service does retain a 90-day versioning history which also counts against your quota. If you have de-selected items from backup the purge option will let you delete them from online storage.
NOTE: Please ensure the items you select to purge as no longer needed since purging content is a permanent action.