RadButton peforms a duplicate request (the second request aborts the first one) when the following conditions are met: -The page is opened from Visual Studio 2008 - A RadButton exists on the page and the form is submitted when a text box is focused and enter key is hit. -Default button is not set to the form. -RadButton's UseSubmitBehavior is set to true -.NET Framework 3.5 is used. -The browser is Internet Explorer. The workaround is to either set Default button for the form or set the UseSubmitBehavior property of the RadButton to false.