Hi CSearie,
Unfortunately, we can not tell you more than for you to re-connect it the same way you did first time.
Tell us everything about your case :
Was the shave over NFS ? AFP ? SMB ? iSCSI ? ...
How did you mount it first time ?
What is the error message you receive now when you do the same ?
Can you reach the FreeNAS box at all from that Mac ?
...