I have got a tricky problem with VS2012 and EF5. I have posted the full details on the MSDN forum, see: http://social.msdn.microsoft.com/Forums/en-US/adodotnetentityframework/thread/c63bf034-f205-4b4e-82e0-40b1c3fca71d.
However it seems that the EF team are now recommending we also post on here as well, so I am.
Many thanks.
If this is the EF Designer Power Pack then it is not supported. See this for more details:
http://entityframework.codeplex.com/workitem/499