Mine's started doing this too, though I've not used the vid cam since July so I'm not sure how recent a problem it is.
My phone is rooted, but as the post above isn't, I'm guessing that's not the cause in itself.
When I try to record a vid, after pressing the optical button, it freezes after a couple of seconds and then just resets. Tried messing round with the settings but no effect.
Anyone any ideas what could be causing it?