invalid HTTP response code ‘0’

I am trying to make use of a script that uses CPAI开发者_JAVA百科NT and I keep getting the error above when I click on favourite an item (a 5 star rating system).

It looks like it is making an AJAX request but I can not see this from my Firebug to debug this - why is this the case?

More importantly what does the error code 0 mean?

Thank you all for any help

A response code of 0 from XMLHttpRequest can mean that you are being blocked by the same origin policy. Make sure that you are using relative URLs for your AJAX requests.

You may also want to check out the following Stack Overflow post for one possible solution to workaround the same origin policy:

• XMLHTTPRequest.status returns 0 and responseText is blank in FireFox 3.5