Sounds like VS has installed it multiple times.
Remove all references to ASPNetFLash from you toolbox and project. Restart and try again.
From our downloads page there is a link to download the DLLs in a ZIP file.
That way - you can install manually by- darg-and-drop into your toolbox.
Please trust that this is VS2008 compatible. It was developed on VS2008 - and most of our users use this IDE.
http://www.aspnetmedia.com