Error in Upgrading Silverlight

Question

I've inherited a fairly big project that needed upgrading from Silverlight 2 to Silverlight 4. I recently ran into an error trying to test the project.

Microsoft JScript runtime error: Unhandled Error in Silverlight Application Set property 'System.Windows.FrameworkElement.Style' threw an exception. [Line: 257 Position: 27]   at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
   at ESM.Visualization.MainPage.InitializeComponent()
   at ESM.Visualization.MainPage..ctor()
   at ESM.Visualization.App.Application_Startup(Object sender, StartupEventArgs e)
   at MS.Internal.CoreInvokeHandler.InvokeEventHandler(Int32 typeIndex, Delegate handlerDelegate, Object sender, Object args)
   at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)

I think there might be some files that went missing between Silverlight 2 and 4, but I'm not sure where to start looking for changes to fix. Any help would be appreciated.