From the ADO.NET Team blog:

Late last week, after bits had been finalized, we found a bug in the ADO.NET Entity Data Model Wizard that shipped with Visual Studio “Orcas” beta 1. The problem has now been corrected.

Please download and install the patch available at: http://www.microsoft.com/downloads/details.aspx?FamilyID=f69e9eb8-0ebd-4fba-a4cc-2050297ba75b&displaylang=en to fix the problem.