I've found out that jquery 1.4 and 1.4.2 both make the browser show a popup when in an ajax request the server answers with 401 Unauthorized.

Is there any way to change this behaviour in jquery 1.4? I want my code to process the error, not an authentication popup in the browser.

As I found no way of avoiding this, I had to change to jquery 1.3.2, which calls the error function specified in the ajax request.