Spears can't couch, so you have to use a lance. To be sure the weapon you have can be couched, when in battle look if there's a little white dot next to your weapon's icon (it turns red when you deliver damage or raise it from couched).
Finally, this mod works with version 1.143, so using version 1.152 can cause some little bugs like music and archers' behaviour, maybe this one is also due to the version you are using.
P.S. IMHO, using couched lance is a waste of killing in this game. In the time you need to reach a certain speed, aim an enemy, hit, wait and charge again, you can kill many more enemies just holding left mouse button and releasing toward an enemy (simple thrust damage).
This way: you don't need to keep a minimum speed like for couching; you don't waste a charge if you hit a shield; you don't have to wait before couching again; finally you can run behind an archer line from left to right (it's better because enemies are on your right side, where your weapon is) and kill at least 3 of them one after another. This last thing works also with infantry as long as they do not turn around to face you, but just a few of them will do it and they won't aways have a shield and use it.
Couched damage is good against lords or strong enemies, but i rarely use it.
