Thanks Twist,
I will take the starter off tonight and have a look at that. I also read in my manual that I should inspect the starter clutch (they say it should turn freely in one direction, and not at all in the other)
I am only guessing that it is the starter that is jamming the engine. I suppose it could be any number of things. I know the Cam chain has been making a rattle for a little while, I was going to replace the Cam Chain Tensioner. is it possible that the chain rattled itself loose and ground the works to a halt?
So much for summer riding...
Hopefully it's something that can be fixed without too much work.
Another thing that may be helpful in diagnosing the problem. My bike was leaking oil out of the seal where the Tach enters the engine. I replaced the oil seal and O-Ring. and as soon as I rode it after that it was making a bit of a rattling noise (that I mentioned in my first post) I figured I had done something wrong and that the tach cable was rattling because it was loose or something. When the bike seized I first thought it was a problem with the tach spline (as I had just been monkeying with it) but it came out smoothly and looked fine, and even with it out the bike wouldn't turn over. So it may just be a coincidence that this happened right after I replaced the seals.