Volumes > Click on the jails storage > at the bottom left one of those buttons is for permissions. Go ahead and click it, and set it up as applicable to your setup.
Running FreeNAS in a VM with less than the recommended hardware specs is not a very good testing environment. Just double check your network settings and make sure they're setup correctly as well since it's not a hard-line and probably either VirtIO and/or bridged.
I get the same problems when running a vm off my MacBook with 8gb ram. Don't won't to fork out the cash if it doesmt work but guess will have to bite the bullet
You can make a FreeNAS boot USB and test it with a real machine temporarily. I'm not saying go out and buy a whole system, just saying FreeNAS isn't built to be run in a VM. Also, if you got the same error on two different setups, maybe research how you're setting it up and if it's the correct way per what you're trying to do.