Your characters may need to have the SP required to do the move when you're trying to learn it.
The surest way to learn the move is to stick a Foreboding skill on one or more of the characters involved in the combo. It's a C-Rank Mental skill. When you get your turn in,a line will be drawn to the characters involved in a tech when you have an opportunity to learn it. Then you use the move and it WILL work. If you really can't get the move, invest in a Foreboding.