Hi,
Like was said above, YOU MUST have the latest software in both heads for Interlink to work properly. Since the new 2010 and 2011 units came out Humminbird has been have lots of problems with the legacy Interlink box. It has taken several releases of 5.xxx and above software to get things going again. I’m sure they would love to move onto the Ethernet style of unit communication and leave the Interlink box behind (Humminbird will not dump their legacy box support (if they can help it >>> unlike the other guys)).
Below is some information that might help resolve your situation.
This is some instructions I found on a chat board to restore your Interlink connection:
“Backup the waypoints by Saving All Nav data.
Stop participating on both units.
Delete All Nav Data on both units.
Start Participating on one unit and when prompted tell it to KEEP DATA ON THIS UNIT. This will clear and reset the Interlink by sending 0 waypoints to it.
Reload each unit with the SD card. This will also reload the Interlink.”
Here are some useful FAQ links from the Humminbird website:
< http://www.humminbird.com/Faq.aspx?TaxonomyId=102A3078 >
< http://www.humminbird.com/FAQ.aspx?ContentId=3080 >
Good luck,
Roger