Screen Freeze On Option Selection (Re-Post)

Just got some feedback from 2 customers on a glitch in our cart. On some products but not others, as soon as the first option is selected, a small black box appears in the middle of the screen. It looks like the box that would normally have the wheel indicating its processing the input. It doesn't disappear and locks any further mouse clicks. It happens in Firefox & Internet Explorer but not Chrome.

PS - This is a duplicate of a thread started in the Multi Vendor forum but since I couldn't attach the screenshot that I've attached here for visual clarity of the problem . That forum had no section to 'Attach files'

Add to the above - it's happening in Chrome as well.


Problem solved - by CS tech support. It turned out to be a bad line in the .htaccess file. A Redirect 301 that was blocking the cloudzoom.js and the cart access.