Are you on a stance? I noticed something weird while raiding. In winter you get reduced movement and if you have that stance it will say you don't have any movement points, but actually you do. You just have to get out of that stance, move, and come back to it (keeping in mind the % needed to go back into the stance of course).

I believe you should be able to move while in the stance but something must be off with the script and it reports 0 movement points while actually it isn't.

I did notice it seemed to happen in winter, and changing stance did fix it once. I haven't had it happen again in my current game.

it seems to happen in winter regardless of 'setting' a stance- since I recruited the turn before, I was in 'muster' and the next turn was a harsh winter and I had no movement. This does not seem to affect the AI, however, as they have unlimited funds and will just recruit a massive mercenary army and seem to have normal movement (not reduced from winter)