Check the Interlink status screen and note the number of waypoints and routes in the Interlink, Shared (Unit 1 and Unit 2) and Locked (Unit 1 and Unit 2).
You may find that the Interlink and both units show exactly the same number of waypoints and routes. Or, one may show a different value but you are still being asked to merge the data each time you turn the unit on. Please take the following steps to "reset" the Interlink.
1. Save your NAV Data to a SD card for backup. If possible load them on another unit or a PC using Humminbird PC. Verify that you have your data securely backed up before proceeding.
2. Go to the Interlink menu and select Stop Participating on BOTH units.
3. Go to the NAV tab on one unit (you will need to be in Advanced User Mode) and select Delete All NAV Data. This will clear the unit of all waypoints, Routes and Tracks. 
4. On the unit you just cleared, go to the Interlink option under the ACC Tab and select Start Participating.
5. The unit will now ask you to Fully participate in the network. Press your right arrow.
6. When asked how you want to participate select Keep Data on this Unit. This will send null NAV Data to the Interlink and rest.
7. The Interlink and unit will now sync. You will see the message Interlink Sync in Progress.
8. When the sync is complete, go to the other unit and select Start Participating.
9. When asked to participate - right arrow to acknowledge.
10. When you are asked how you want to participate on the second unit tell it to Keep Data on this unit. This will load the Interlink and the other unit previously cleared with the NAV Data from this unit.
11. You will again see the Interlink Sync in Progress message.
12. As the sync is going on you can use the Interlink Status option to view what is happening with the sync. You can see the data being populated on the Interlink and the first unit.
13. When the sync is complete, turn off both units and then turn them both back on. Both units should now be in sync with the Interlink and there should be no messages displayed on your units.