This is a problem which happens when your Viper-II (Medallion) controller loses its security-handshake with your engine’s ECM. We have researched a fix for this, so please see this post, download the document, print it out, and keep a copy in your boat’s dry box. It may save you from a tow someday, and prevent a trip to the dealer, costing you time and money.
https://www.facebook.com/groups/ChaparralVortexBoatOwners/posts/2116335005338907/