ummm.... is the lockup occuring outside of the orthographic view? If it is, then you have a real problem.
If however, the planar lock is happening while creating the curve inside one of the orthographic views, that's supposed to happen. its so its locked into a single plane. Actually helps make cloth panels. I don't know if you can disable it, but I wouldn't really want to, anyways (check preferences). If you want to make a curve that moves in three dimensions, try using another view in conjunction with that.