It's taken a little while, but having now successfully learnt YouView codes (not listed) to SAT/CBL, and DVD codes to both VCR and CD, I'm hoping your problem is merely one of a slight misinterpretation of the instructions - please don't be offended, it took me several goes to get it right.

Using the DVD device power on/off button as an example...

Key:
LCD screen - TV
Button Press - set

DVD -- set -- CODE -- cursor left or right -- LEARN -- OK -- L_ST -- OK -- IR IN signal transmit icon (bottom right of LCD screen) flashing.

• Place original and 991 remotes facing each other, approximately 3 -5 cms apart.
• Press power on/off button on original remote and hold until the signal transmit icon stops flashing and KEY IN is displayed.
• Press corresponding button (power on/off) on the 991 - the display will revert to IR IN and flashing icon.
• Repeat process for other buttons or to exit...

set -- LEARN -- exit -- DVD

Try it and let me know how you get on.