In Music Manager, I believe you can "save changes without ejecting," which will update the DMS. Then you can close MM and use the "safely eject hardware" icon to remove the DMS.
Eject will fail for any number of reasons, most commonly because of antivirus programs, but it can also happen if you have any other windows or programs open. You should be able to kill Norton and anything else using the Windows task manager. If you search around on the net you should be able to find which processes are related to Norton, and kill all of those.
It could be specifically because of the Norton protection on the recycle bin. Right click on your recycle bin and configure it to use different settings per drive. On the Phatnoise partitions, select "Do not move files to the recycle bin." You may also be able to turn off that protection from within Norton.
As a side comment, Norton is a terrible antivirus solution. My friendly advice is to switch to something less demanding on your system and more effective, such as Avast!, TM PC-Cillin or AVG.