I have understand your trouble; I have one answer for you. Really the trouble is 64-bit pc. According to me there must be 64-bit edition of aspnet_regsql.exe on 64-bit running system. When you set up 32-bit software on 64-bit operating system, it will never ever operate for you. Or else convert your OS to 32-bit, since 32-bit machines wonít have any trouble with SilverLight Application.