This errors pops up as soon as you switched from Visual Studio 2008 Beta 2 to Visual Studio 2008 RTM. Here’s the exact error:
System.InvalidOperationException: An item placeholder must be specified on ListView ‘ListView1’. Specify an item placeholder by setting a control’s ID property to “itemPlaceholder”. The item placeholder control must also specify runat=”server”.
To fix this, replace every itemContainer occurrences with itemPlaceholder, recompile and it should work. Also note that the control which is targeted as itemPlaceholder does not render CSS or other attributes anymore, you have to set them on surrounding HTML tags now like a div or ul.