Unable to run forward sometimes.

Sometimes my character is running, and suddenly stops, as if he's run into an invisible wall. If running, his legs will continue to move as if running, he just won't advance forward. If on a mount, the same thing happens. It will continue the movement animation, just without actually going forward.
This is always in the middle of roads and things, and a moment later advancement resumes. So it's not that I ran somewhere I shouldn't and hit an actual invisible barrier.

Sometimes after this happens, I get an error that shuts down the game (microsoft c++ or something), and sometimes I don't, but a little later I'll run into another "invisible barrier" again while running somewhere.

It can happen literally anywhere. Just now it happened as I left Ul'dah on the way to Black Brush Station on a porter chocobo. Last night it happened an inch or two before zoning into Ul'dah on my own mount. A couple of days ago it happened between Camp Dragonhead and the area where you fight Svara while running on foot.

I can't find any other threads about this (maybe using the wrong keywords?) so I don't know what could be causing it.