I initially had a problem getting the learned
IR signals from my cable box remote to work
through the Pronto.

It turned out the batteries in the cable remote were very weak and I had initially taught the Pronto in my living room under bright daylight.
With fresh batteries and in a darker room, I relearned the signals and no problem. Also, make sure there is no misallignment between the
Pronto learning eye and your teaching remote.
As an example, my cable remote is very thin so
if it is placed too close to the Pronto during
learning, the windows are really offset. So try
those three things.

I think even though the Pronto may come up with
'OK' for a given IR signal your sending it, that
doesn't necessarily imply that it is checking
whether or not the signal is valid for the device.
I think as long as it receives a minimum signal
strength of recognizable frequency, then it
comes up with 'OK'. Of course other IR junk
from room lighting or misallignment etc. could be
mixed in.

Good luck.