Ok don't worry – seems there was a line length issue with something in the way the text was formatted in the contents page – very odd and unexplained but at least I can start work now...
Any thoughts still helpful though...
Lines that can't break usually have hyphenation disabled in some way (perhaps all the ords are too short to break) and spaces that connot break, either because non-breakiing or fixed-width spaces were set, or the No Break attribute is set. I've also seen a case where left and right paragraph indents combined made a column too narrow to hold text above a certain type size.
It's often easiest to diagnose this kind of problem in the Story Editor where you can select and eamine the first line or two of the overset text.
Thanks Peter, yeah it looks like that's the general gist of the problem. Cheers