Which version of Data ONTAP and which version of Storage Manager are you running? If you login to the filer's administration console using the same monitoring (not scanning) credentials provided to Storage Manager, do you see the list of CIFS shares and their respective folder paths? Have you tried providing another monitoring credentials to Storage Manager?
BTW, you will not see any data in the NAS shares tab until the scanning results have been reported back. So, the first step is to see the list of CIFS shares in the 'Assign Remote Shares' settings page