Okay so this is a strange issue.
Code taken from another working site and moved. All instances of the original domain have been replaced with new domain, in both code and database.
New site has same code, db etc .. but as above, changed to new URL ..
on the new site, the drop downs for currency select and also the drop down for size (configurable product) don’t work.
if i install just a base install of magento on the server then ajax works .. so it must be buried in the template. Any thoughts?