Do you have a Navionics map card in one or both of the units? If so, remove it and see what happens.Have you set up an account on-line at the humminbird web site and registered your units? If not do that, register your units and download latest software. Youll need an SD card to upload the software onto your units. Make sure you get software upgrade for BOTH units. If you only do one it wont work properly. This is all pretty easy to do, just takes a little time.Then contact humminbird and theyll give you directions how to reset the interlink.