We just installed a Windows Server 2012 R2 to provide simple workgroup file sharing for 20 users.
All users running 10.8 and 10.9 are 100% solid accessing SMB file shares on the 2012 server.
But some Yosemite users are unable to attach over SMB. The error they get is "Access to your account on the server "[servername]" has been denied. Contact your system administrator for more information."
All users are able to access the server using CIFS.
The same user can log straight into the same server using SMB on a different Yosemite computer.
A Yosemite computer that is unable to log into the 2012 R2 server using SMB, *is* able to SMB into a 2008 R2 server.
We wiped a Yosemite system that doesn't allow SMB access and installed an OS from scratch. SMB still denied with the same error.
All Yosemite Macs are running 10.10.3.