We're improving the error code. Instead of "Can't activate a TurboFloat key." it will say: "Can't activate this request because the product key is for TurboFloat Server. However, the customer is trying to use the product key with a version of your app that uses TurboActivate. Either correct the customer, or edit the key to make it for use with TurboActivate."
Short answer: don't try to activate a TFS key in TurboActivate (or vice versa).