Fix for issue with ADO.NET Entity Data Model (EDMX) Designer not opening

I have noticed that when I double-click an EDMX file after closing it first, that Visual Studio 2008 (with SP1) does not open the ADO.NET Entity Data Model Designer. Looking on the internet there are apparently more people having the same issue but so far the only workaround is to open it with the XML editor first, closing it and then reopening it by double-clicking:

• http://thedatafarm.com/blog/data-access/can-t-open-the-edmx-file-in-the-designer-here-s-the-workaround/
• http://devio.wordpress.com/2009/11/06/entity-designer-opens-edmx-file-only-once-and-other-vs-bug/

Using Process Monitor, I saw that the value LinkedEditorGuid for the EDMX designer is not available on my machine:

So this is what I tried and it seems to have solved the problem on my machine (this is for Windows XP x64):

1. Start the Registry Editor
2. Navigate to the following key: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\9.0\Editors\{c99aea30-8e36-4515-b76f-496f5a48a6aa}
3. Add a new String Value named LinkedEditorGuid.
4. Set the value of LinkedEditorGuid to {FA3CD31E-987B-443A-9B81-186104E8DAC1}. (this is the GUID for the XML editor)