The clue is likely that you can't create files (how about folders?) Sounds like "write permissions."
Noted at http://www.lagesse.org/freenas-tutorial-for-windows-users-part-two-configuration/ the problem I find today is that many won't use tutorials or guides. They dismiss them if they are for the prior version even when the basics still apply.
Let me put it another way. The basics of users, permissions and such tend to upset new networking folk. While the days of wide open shares are long gone, I find we have to repeat why that was abandoned.
I have been trying to set up NAS in my home and have come to a halt at configuring freeNAS to work. I have got as far as setting a static IP, creating a share, activating CIFS, creating groups and users. After all this the share is visible in windows BUT when i enter using a the user and password i cannot create files. :S? Can anyone see the problem or offer me step by step instructions for freeNAS 8, all the documentation on google seems to be older versions of freeNAS.