You might have an machine authentication issue against the domain. Try removing and re-adding it.
I have to assume I followed your recommendation. Assume, because I was not sure how to "removing and re-adding it.". Soo, I went to control panel/system and changed machine name ... no joy. Changed workgroup name ... no joy. Did this with all the required restarts. Went back and put everything back to original. No joy.
THEN, I noticed and ran 'Network Wizard'. That did something, because I now have a 5th network device ... one I have seen before, but not in a long while. When I try to connect to it, I get an error 0x80070035 Network Path not found. The device is BRN008077035.
Back to the NAS problem ..... Still rejects credentials. When I look at its properties for the only folder on the drive, I get a window "You do not have permission to view or edit this object's permission settings).when I click on the SECURITY tab.
Hope this info helps a little. Thank you for your attention. I am no network expert.