Analog film photography and cameras

I got this on film recently, really badly but only on one or 2 frames and I was agitating well.
Any ideas?

Edit: Here's the worst image http://www.flickr.com/photos/andephotographic/5580462763/ and yes I know it's also got a massive light leak on it.
The previous image in my photostream is the only other frame where this was visible.
Is it possible the film wasn't quite as it should have been in the spiral and these frames didn't get proper flow of dev around them?

Cool picture shame about light leak, are you sure you agitated tank with fixer bath too? The vertical streaks on the sky can be poor/ if any/ agitation during fixing stage, or light leaks. I can't tell from this pic what is the case but you could try fixing bath again.