Ok. That error basically is a "your database is ruined" type of message. It's a pretty serious problem that none of us would want to see happen. I just wanted to be sure that wasn't something I might see myself.
If you aren't at the minimum specs (mostly 8GB of RAM) you can expect random problems as a result. So if you want to see FreeNAS work properly, you should make sure you have 8GB of RAM.
It would suck to test an OS that is horribly prone to random unexplainable errors and you think FreeNAS is just poorly written. ;)