TV 10812 probably has the correct IR signal for Enter programmed to the OK/Select button. However, the Comcast and Access remotes are intended to control a cable system, so even in TV mode, the remote sends the digit, ch+/- and Enter signals to the set top box.
There are two ways to defeat this.
1) Turn off Channel Lock. See the 9XX comand
2) Assign an EFC for the Enter signal to the TV device mode.
1) Press TV
2) Press Setup until 2 blinks
3) Enter 994 (2 blinks)
4) Tap Setup (don't hold it)
5) Enter 00069
6) Press OK/Select
The remote should blink twice, and the OK button should work in the TV mode.
Use 1) unless you're really going to use the remote with a cable box.