Hi
Thanks for your answer. I don't recall making any changes to my document in inDesign like this. All I did was change my logo and a bit of text (and one slight change to a paragraph style) - The latter seeming the most dangerous according to your answer. I think I noticed it was producing CSS and I switched it off..
I exported the same as I always did.
Also as I said a previously used epub that converted to mobi stopped working too...??
Also, why do KindleGen do a better job (only in the respect it doesn't hang?)
I will have to research why it has produced fixed html (what this means) and what settings I can use in Indesign to stop this problem

Can you point me to some further information. I personally know what CSS is and where possible I switch it off - cause I don't know how to use CSS - and I dont want to either.. LOL