When trying to compile a project in Microsoft Expression Blend 4 I got the following error:
myproject.sln.metaproj : error MSB4126: The specified solution configuration "Debug|HPD" is invalid. Please specify a valid solution configuration using the Configuration and Platform properties (e.g. MSBuild.exe Solution.sln /p:Configuration=Debug /p:Platform="Any CPU") or leave those properties blank to use the default solution configuration.
To resolve this issue you need to remove an interfering environment variable named “PLATFORM“.
This can be done in three easy steps (without hacking the registry)!
1. Open the Environment Variables dialog.
On the start menu Right-Click on “Computer”, select “Properties”, then click on “Advanced system settings” in the left column and finally locate and click the “Environment Variables…” button.
2. Remove the PLATFORM environment variable.
In the System variables list locate and select the PLATFORM variable and click Delete to remove it. Hit OK to close the Environment Variables dialog box.
3. Make it work.
Now restart Blend and you will be able to compile your projects.