My guess, is that your "server" (desktop) is at least 7+ years old.
IMHO, it's so old, that one can't expect it to work with the latest version FreeNAS.
You might want to try v8.3.2 or maybe? a 9.1.x version. But I wouldn't even attempt to run 9.3.
As an aside, I have/had two similar vintage systems. I gutted/rebuilt one in late fall and am still migrating programs/data from the 2nd one to new one. Neither ran as "servers" just a desktop OS.