Maybe just bad luck on my part, it failed every time I tried it. Tried on 4 or 5 different flights and types of aircraft.

On another topic ...

You were talking about using the mobile.united.com to get the registration number in the future by playing with the date in the url??). If all you want is the aircraft type, there is a weekly aircraft type download for wide bodies on unitedcargo.com. Admittedly for 772, there is the constant possibility of an aircraft swap, but at least it shows you where the IPTE 772 are supposed to be flying.