PanMan,
4.950 is the latest software version for the 997 units. I did not know they already put the 5.210 for the 858 units. Let me know if you need the older software for the 858 by sending me a direct e-mail requesting it.

Just thought about this: try calling the Humminbird Customer Resource folks at 1-800-633-1468 and find out the steps to reset the InterLink.
Was the InterLink connected to the 858 unit when you updated it?