Cannot add event handler because code element marked as read-only

解决步骤如下:

-Close all instances of Visual Studio

-Delete *.ncb *.aps *.suo *.user
-Open Visual studio and clear solution

-Build solution

答案来自:https://connect.microsoft.com/VisualStudio/feedback/details/105469/cannot-add-event-handler-because-code-element-marked-as-read-only