It is usually something simple and will be in the steps in this KB... go through all these and make sure you have time within 5 minutes of the DC, the default pcuser unix user (unix user and group create), then have a default unix user for cifs or the shares won't work "vserver cifs options modify -vserver -default-unix-user pcuser" ... not having the default unix user (even if cifs only) is the most common reason it doesn't work. Work through this KB step-by-step and I bet it works for you. Not all the steps are needed (nis, usermapping, export policy, etc) when cifs only, but you must have the unix user and the mapping.
Data ONTAP 8: How to create a CIFS server in Cluster-Mode
https://kb.netapp.com/support/index?page=content&id=1010569