There are currently two version of WCF RIA Services:
- WCF RIA Services Beta for Visual Studio 2008 SP1
- WCF RIA Services Preview for Visual Studio 2010
The first is compatible with Silverlight 3 and the second with Silverlight 4. From what I understand, Microsoft will not update the current Beta for Visual Studio 2008 SP1.
In other words:
- Using Silverlight 3, you’ll use RIA Services bits that will stay in Beta forever.
- If you want to use the final (and supported) RIA Services bits, you’ll have to develop for Silverlight 4, meaning upgrading to Visual Studio 2010.