i installed the august 2011 windows phone silverlight toolkit from <http://silverlight.codeplex.com/> . 

After installing (and restarting the computer), i try to refference the silverlight toolkit( located in `C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.1\Toolkit\Aug11\Bin\Microsoft.Phone.Controls.Toolkit.dll`) in my VS project.

When i try to do this, i get an error saying "`A reference to a higher version or incompatible assembly cannot be added to the project`". Why is this and how can i fix it? My VS is Visual Studio express edition for windows phone.

To be noted, in the reference list, i also have included Windows.Phone and Windows.Phone.Controls (refering to the "higher version" maybe)