I was banging my head against a wall for weeks when that happened, trying to figure out why all my Mac users suddenly couldn't access the shared network drives at work. Mac users being as they are, they defended the macs furiously and spent a week or two pointing fingers at me and my network capabilities.

Oh how I rejoiced when 2 weeks later Apple released a changelog for a small quiet update stating that they had 'fixed' samba connections, even though they had never announced anywhere that they had broken them in the first place. The Macs started connecting to network drives again and all was well, and the mac users all went very quiet for a long while.