Problem installing Silverlight SDK in VS2010 Beta 2
Many have already started trying to use the latest release of VS2010 and received messages that the Silverlight 3 SDK could not be installed. This is a known issue and can be easily circumvented.
The problem is that you have Silverlight 3 RTW installed, SDK version 3.0.40624.0. VS2010 is trying to install Silverlight 3 GDR2 3.0.40818.0, which does not automatically update. Just GDR and can not install and gives an error.
This case does not particularly affect the development of Silverlight applications, many have already confirmed this. However, some problems may arise as a result of using the Silverlight 3 RTW SDK. To fix the problem, you need to uninstall the Silverlight 3 SDK and install the latest version .
The VS2010 team is already working on a solution to this problem in the RTM version.