I'm having the exact thing happen to my MKZ.Anyone having an issue with the Adaptive Speed Control displaying an error from time to time.
Adaptive Cruise Control Not Available
When this happens I also cannot switch over to Normal Speed Control as part of the Driver Assist settings.
I can stop, turn off and exit the vehicle and then restart it and it could re-appear.
Later the next day (after several stops) or the next day it may start working again.
This has now happened on 4 different days, while also working inbetween the the errors.