Thanks Paul,
The maxfile is attached above (twice for some reason) but I've attached it to this post again in case there was a problem with the previous file. Let me know if you still can't see it.
I have checked and all the vertices are set to bezier. To get my path, I drew a circle, and used and edit spline modifier to chop it where i wanted. The gaps don't appear where a vertex is, it appears to be random.