Found a solution for my problem. This Microsoft KB explains it and offers a bypass: support.microsoft.com  
Hi everyone, yesterday I noticed that I can't access my CIFS shared folders. It's asking me for a user and password but whatever I type is incorrect but it shouldn't be. Connecting through computer management also says I don't have permission (I'm the domain admin). I have admin access to the EMC Unisphere and access with the service account through SSH. I tried rebooting the system, re-imageing and re-adding the shared folder server to the domain. I also tried enabling NFS but same issue with no permissions. Nothing helped, it's like the share permissions are lost. The only thing I need is to recover the files from some of the shared folders. Is there any way to access the files?
EMC VNXe 3300 Shared folders issue