I'm running a Mac with OS X 10.11 that's backing up to a DNS-325 using Time Machine. Recently, Time Machine stopped backing up, and I realized it couldn't connect to the NAS. I also can no longer connect to the NAS using the "Shared" links in the Finder sidebar. Both the SMB and AFP shares show up in the sidebar, but neither of them work. If I try using "Connect to Server", SMB will work fine, but AFP won't. It will ask for login credentials but will eventually give me an error message.
At first, I thought it might have something to do with El Capitan, but I also tried it on an old Mac running 10.9 and the same thing happens. I've never had connection issues on that old computer in the past.
I've tried rebooting the NAS, restarting the AFP and Time Machine services, and creating a new user. I'm running firmware 1.05.
Any thoughts?