Hi.
i entered the serial number of another roku ultra that i have and it still says the same thing.
The serial number submitted is incorrect. The serial number can be located on the back of your Roku Streaming Stick.
The extender cable is only for sticks and would do absolutely nothing for an Ultra. For the record, the "serial number" written on a Roku device may or may not be a real serial number in spite of what any Roku documentation says. It may be a "Device ID" which is not the same thing.
For your remote problem that appears to be affecting a device that isn't a stick, you might want to try using a different Wi-Fi channel on your router and don't use "Auto".
