I'm actually having the same issues as Shawn. No non-Mac computers can connect to the new Mac Pro server (10.8.4) using SMB. Mac users can use SMB or AFP without issue.
Here's a screenshot of the message Windows users are seeing:
Can someone point me in the right direction on how to get this fixed? This is urgent!
this link to lion server might help
i tried most of it and finished by creating local users for each windows user ( Mac server not part of the active directory)
they can all log in but if you make a mistake in the credentials you'll get the permission error you posted and you are screwed until you reboot the windows machine and type the correct credentials.
Sounds like an issue that might be related to Windows LSA settings...I believe the version of SMB is differnet between 10.5 and 10.8, so you may not of needed to modify the window lsa settings on the clients before. You can check out http://macs.about.com/od/macwindows/ss/sharemacfilesvs_7.htm for info on how to correct the registry settings for Windows LSA.