Microsoft Visual Studio 2008 SP1 Beta was released this morning.  It is not compatible with Silverlight Tools Beta 1.  The good news is that Silverlight Tools Beta 2 is coming within the next few weeks and offers complete support for VS08 SP1 Beta.

To install and evaluate VS08 SP1 Beta you'll need to uninstall Silverlight Tools and KB949325. For a detailed description checkout the post on the Visual Web Developer Team blog at:

Error installing Visual Studio 2008 SP1 Beta and Silverlight Tools Beta 1