After you integrate a NAS into your domain you will get permission errors when trying to mount the SMB share using CIFS.
Solution
You have to use add the domain parameter from now on:
If the user is a domainuser:
mount -t cifs -o username=USERNAME,password=PASSWORD,domain=DOMAIN //10.10.10.10/path/ /mnt/MOUNTPOINT
If the user is local on the nas:
mount -t cifs -o username=USERNAME,password=PASSWORD,domain=. //10.10.10.10/path/ /mnt/MOUNTPOINT
Cheers,
Ori