I have just installed a clean Windows Server 2008 R2 with latest Service Packs,
SharePoint Server 2010 with June 2013 CU , Visual Studio 2012 with Update 3!
I see the problem not only with sandbox visual web parts, it happens when I create a new visual web part Project (C# with SharePoint 2010 visual web part template) then I try to compile without adding any control yet, then it again says
The name 'InitializeControl' does not exist in the current context.
SharePoint Server 2010 with June 2013 CU , Visual Studio 2012 with Update 3!
I see the problem not only with sandbox visual web parts, it happens when I create a new visual web part Project (C# with SharePoint 2010 visual web part template) then I try to compile without adding any control yet, then it again says
The name 'InitializeControl' does not exist in the current context.