I think the suggestion would be to get another USB thumb drive, put a new copy of FreeNAS on it, just to make sure you have the latest stuff, then go and try to import your ZFS pool, making sure all the available drives are hooked up and working. If that works, then probably back up the information, then do a scrub, and if that works, then you should be in a much better situation (and can probably switch back to your old USB thumb drive).