A few people have run into a Package Load Failure error after installing the Entity Framework Tools. As a workaround to this issue, please follow the below instructions:

Issue

Visual Studio displays a Package Load Failure error message for Package 'Microsoft.Data.Entity.Design.Package.MicrosoftDataEntityDesignPackage’ when you double-click on a .edmx file

Workaround

This issue is caused by earlier installations of the Entity Framework June CTP.

1. If it is installed, uninstall the ADO.NET Entity Framework Tools CTP from “Add/Remove Programs” in control panel

2. Use gacutil.exe to verify that the following DLLs are not in the GAC. 

a. Microsoft.Data.Entity.Design.dll

b. Microsoft.Data.Entity.Design.EntityDesigner.dll

c. Microsoft.Data.Entity.Design.Package.dll

d. Microsoft.Data.Tools.XmlDesignerBase.dll

3. Use Regedit.exe to check for and remove the CodeBase value from the registry at:

a. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\9.0\Packages\{8889E051-B7F9-4781-BB33-2A36A9BDB3A5}

4. Reinstall the the ADO.NET Entity Framework Tools CTP