Ajax not working on QA but works on Dev

Hi
I am using the following statement to register the ajax functions:
Ajax.Utility.RegisterTypeForAjax(typeof(ProductInfo));
Here, 'ProductInfo' is a class inside an asmx file, which have certain methods that get called from javascript.
The code functions well on my local and the dev server, however does not work on the QA server. When we browse the site in the QA server, and try selecting a value from a drop down list, which should use the ajax function to populate another drop downlist, I get the error "ProductInfo does not exist"
One difference (don& ...