I'm trying to test the example and I always get the error message on subject.

What must be done to resolve this?

Thanks 

hi - dont mean to hijack the thread, but I'm getting the same problem.  I have a dropdownlist within a module.  I have just gone through the document and followed the instructions in that.  I have created the success and fail JS functions. All they do right now is exactly what was in the document ("alert('something' + result + ctx.id);").  I have added the lines in to register the xml and xmlhttp scripts and also added the attribute to the onchange method of the dropdownlist.  Just for testing I put 2 items in the dropdownlist, but when I change the item I get "failed:400 - Specified cast is not valid.(dnn_ctr601_OffersManager_Dropdownlist1)".

Can anyone help with this?