Make sure that Visual Studio is closed, and run the installer file that you downloaded from www.aspnetflash.com.
This choice seems confusing, but it is actually quite simple. If you have Microsoft AJAX installed, or if you plan on installing it before using the control, select Yes, and install the Microsoft AJAX-Ready WebControl. If you do not have Microsoft AJAX Extensions installed and do not plan on installing it before using the control, select No, and install the Standard WebControl.
The AJAX-Ready control relies on the Microsoft AJAX Extensions, and so they must be installed to use this control. However, if Microsoft AJAX is installed, the AJAX-ready WebControl will work in AJAX websites or standard websites, in Update Panels or outside of them. The Standard WebControl will work in every case except within Update Panels, where it disappears.
To download and install Microsoft AJAX Extensions, go to the following link: http://ajax.asp.net/