I have exactly the same problem as the above, unresolved thread. Time Machine backups were working great for months then suddenly stopped and NOTHING I try will work. I also have these specific problems in common:
We had this set up per the installation guide and it worked great for months then suddenly stopped. Any attempt to re-start the backups complained about user credentials not matching. I reset the passwords everywhere I could find so I knew they were all the same, no help
If I delete the old back-up name and create a new one, Time Machine only offers the old deleted one
If I try to change any attribute on the ReadyNAS related to the user id that is for the Time Machine backup, I get this error: "Could not save user info."
So ... no replies which is okay - but I wanted to report back that I ended up hitting the Factory Defaults button via the web browser interface and then just started from scratch. Now both Macbooks are backing up reliably. Will turn my attention to the three PCs that need to be restarted.
Anyway, if there was a more artful solution I missed it but a factory reset was what ended up working for me.
Laurent, maybe do what we did - delete everything and reset the NAS to factory defaults and start over. All our PCs and Macs are backing up without incident since we did that. Including through multiple power outages.
