The Short Version: Every now and then File Sharing on the target machine running OS X Lion quits working. I must disable and then re-enable File Sharing to get it working again. So far I haven’t found a permanent fix.
Today I discovered that I could no longer access shared files on my iMac from a MacBook Pro via SMB File Sharing. Both systems are running Lion. The file sharing was working only a day prior. This problem was rather odd. I could access file shares on other machines from that Mac without a problem. I could also access that Mac via Screen Sharing using the same credentials that File Sharing wasn’t accepting.
I’m not sure what caused this problem. The only major change I made on the iMac since yesterday was to run a Full Defrag using iDefrag 2. I don’t know if this actually caused the problem (or if it even could). While troubleshooting the issue I repaired permissions on the drive, but that didn’t make a difference.
Though the short name, originally established under Snow Leopard, for the account had been working I tried using only the long name. That didn’t work either. Every time I entered my credentials the login prompt shook to indicate it didn’t work.
Finally, I just went into the File Sharing Options, unchecked SMB (AFP wasn’t checked to start with) and saved this change. This turned off all file sharing. Next, I went back into the settings and re-enabled SMB File Sharing.
Despite the fact that the system settings weren’t any different I can once again access shared files over SMB. My best guess is that something hadn’t been fully re-enabled. Perhaps during the defrag process some permission was changed that prevented the sharing from working. By disabling and then re-enabling the service it may have re-established the appropriate file permissions. Of course, that’s just speculation.
Updated 11/24/2011: The fix wasn’t permanent. The same problem cropped up again and, as before, the same solution also corrected the problem.
Updated 06/09/2012: Yep. It still happens despite various system updates that have been released since. Every now and then I’ll attempt to connect and then find that I have to disable and re-enable the service to make it work again.