I have a dataset and created a group in freenas and assigned it as owner of this dataset, I created an account in freenas with the same name and password as one of my Windows logins and added it as a member of this group which is owner of the dataset. I created a CIFS share pointing to this dataset. I log into 2 different Windows PCs with the same credentials and password. One can write to the share the other can't. If I look at the permissions on the folders the group is listed there with write permission.