Recently I had to reinstall my laptop, so I also installed VS 2008 and Expression Blend. Expression Blend is a better WPF designer and VS2008 still has to lot of bumps to fix like frequent crashes on WPF, showing errors that are not there etc. So I tried to use Expression blend but it seemed that when ever I tried to open a VS2008 project I get an error message. The message tells me that the project file is invalid because there in an Import directive there. When I looked closely I found this
<Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
When Blend finds this tag it cannot load the project. So I tried removing this line and the project loaded with errors. Then I downloaded the Service Pack 1 for Microsoft Expression Blend from this location and installed and Walla! All my problems were gone. Please note that according to MS installing Blend 2 September Preview will also fix this issue.