Hi,
I've just recently started having a similar, if not the same, issue.
I was in the process of performing a burn-in of 5 new WD 3Tb Red Drives. After running the smartctl command for the long test I left the server to do its thing [estimated 393min for each drive]. I was performing the test concurrently on all five drives. I was using PuTTY to access the server via SSH.
After a while I came back and noted that PuTTY was inactive and the WebGUI was experiencing an error. THe router confirmed that the network connection to the server was gone. After a reboot the connection was restored [according to the router] but I am still unable to login via the WebGUI or PuTTY [using SSH]. After two reboots Firefox and IE are unable to connect [they time out]. I have tried both of the network LAN and can confirm I haven't got the LAN IP [192.168.0.5] confused with the IPMI IP [192.168.0.12].
I've attempted to boot into a previous version of FreeNAS 9.3 but this hasn't helped. the boot menu confirms that the webgui should be accessible from 192.168.0.5.
Using KVM to jump to the boot up screen, I did note a bunch of text after the boot up menu. Text such as:
freenas kernal: arp: 0c:c4:7a:6a:5a:6c is using my IP address 19.168.0.5 on epair0b!
freenas kernal: arp: 02:63:46:00:09:0b attempts to modify permanent entry for 192.168.0.5
0c:c4:7a:6a:5a:6c is the MAC address for the FreeNAS LAN. I do not currently know what the other MAC address. It's not being reported from my router.
This appears to occur when I loaded up the Java iKVM window.
I was able to get into the system by rebooting the server. However, this was only temporary and eventually the WebGUI reported "Sorry, an error has occured" or similiar. The WebGUI reported a "The WebGUI address could not bind to 192.168.0.5: using wild card"error. Not sure if this is part of the cause.
Any help in getting access back to my server would be appreciated! :)