I just updated my Apple Watch and now the charger that came with the watch gives me a message that charging with this device is not supported by Apple Watch! What !!!???

I assume you mean the cable with the puck? Try doing a forced restart of your watch.

Have you updated to iOS 8.4.2? If you have and still get this message click on the Get Support link at the top right of this page to contact Apple Support.

What series Watch is it and is that to 8.4.2 and is it the USB c Charging device you are using please or USB a.