As you could have red in my Ajax presentation sheets (http://dotnetpret.blogspot.com/2006/09/ajax-buzz-or-here-to-stay-lecture.html) used webservices must origin in the same domain, but not only that, there are also issues with different subdirectories. Today I sufferd the consequents of this issues, in my test page the ATLAS autocomple control I build worked fine, putting the same control on a webpart and using this part in my on masterpages based portal nothing happend! and worse, no errrors, not even JavaScript error.

To cut the story short. When using asynchronous callbacks in your masterpagebased pages, put your webservice (*.asmx) files in the same directory as the masterpage!!!