Hier noch mal für alle "Express"-Nutzer:
http://msdn.microsoft.com/en-gb/vstudio/aa718685.aspx :
Express Editions:
The VB and C# Express products do not expose the Target property inside the development environment. You will need to carefully modify the project file using a text or XML editor.
1. Close the project and/or solution
2. Select Open File from the File menu
3. Navigate to the project directory, and highlight the project file
4. Press the Open button, the project file should open in the XML editor
5. Locate the first <PropertyGroup> section and add the following line:
<PlatformTarget>x86</PlatformTarget>
1. Save the project file
2. Reopen the project and/or solution using Open Project/Solution from the File menu
3. Continue with development, debugging, and testing
läuft perfekt.