Marketpress broken in more ways than one.

Ok, I had a problem(still do) with a product I purchased off this site. It seems to get customer support we have to pay even more. It's like ford selling me a car where the wheels don't work and then asking me to pay more to get it going! Anyway, rant over. I need help.

My Marketpress is installed on a Multisite and on one site it works and on another it does not.

The two sites are on a global cart. Plugins are almost identical and when I disable all the plugins on the one that doesn't work the fault is still there.

Ok the fault:
On checking out the last checkout on teh shipping page does not go to Paypal but recycles on itself. i.e. it stays on the same page going nowhere. On the site that works with exactly the same cart full of product it works fine.

I am sure it is something silly.
site one:
http://sonneteer.co.uk/home/
site two:
http://sonneteer.co.uk/home/boutique

one not working, two is working.

HELP!