Can't access shares via SMB

I'm suddenly having some permissions problems on our RN316.

Things were working swimmingly, and then I made some rather minor ACL changes to a certain share via the Admin Control Panel. Now none of the shares can be accessed—even after I restore that one ACL to its original settings. In fact, now I can't even connect to the device by hostname in our Windows domain-connected environment (let's call the domain DOMAIN, for purposes of this discussion).

The ACL change I made was to remove the Everyone user and uncheck Allow anonymous access on the Network Access tab. I also changed the workgroup from WORKGROUP to DOMAIN and added an administrative user.

I backed out of all of these changes, but the situation didn't improve. I'm prompted for credentials when trying to connect in File Explorer using \\BACKUP (the RN's hostname and A record in our DNS), and that dialog requires use of a domain (DOMAIN\user). I've tried using DOMAIN, WORKGROUP and BACKUP for the domain part, but none of these works.

I even tried creating a brand new share with default ACL settings. No luck.

Yikes! What's gone wrong here and how can I set about fixing it? I can't do a default, as there're important files on the box that I need to get off first (a temporary condition, as I'm in the middle of a domain migration to a new DC; the timing for all of this is very bad). I could download them through Control Panel, but given the size and number (hundreds of gigabytes and hundreds of thousands of files) that's a task seemingly doomed to fail.

Any ideas?

Thanks,
Jeff Bowman
Fairbanks, Alaska