Were you allied or NAP'd with any AI? If you are, the pathfinding will try to move you through friendly cities, but if the cities are garrisoned, you can't step over them, so the pathfinding freaks out. Yes it's dumb

I once got almost completely stuck due to this (and I still can't figure out how to break a NAP) - I had to resort to casting raise land repeatedly to build a very expensive land bridge AROUND allied cities.

I tend to get wacky unit movement when I'm trying to move to a square that is on the slope of a mountain.  Instead of going to the square I've chosen the unit scurrys off somewhere else.  Usually if you rotate the map, you can get it to work properly.  But there's clearly a bug going on somewhere.  Note, I'm not talking about trying to get to an inaccessible square, the squares I'm talking about are on a mountain side but are accessible, in fact there's often something I'm trying to get to on them -- either a treasure location or possibly an enemy unit I want to attack.

And it is still present in the .76 version, extremely irritating. Maybe we should post this as a bug so they can get around fixing it before the final version is out?