Cannot learn Cogeco DVR zero button

Manufacturer: Arris
Model: DCX3520e-M

I have a Cogeco DVR (made by Arris), and when I try to use the unfolded dock 3 to learn the infrared code for the zero button (ie: 0) from the remotes number pad, the dock displays an error that says “IR Learning INVALID”.

Any ideas on how I can get the infrared code? Or why the dock is throwing an error when I try to get it to learn this one button (it was able to learn all of the other buttons).