There are following steps for resolve this problem. This problem occurred when you copy any mail in any shared folder or Shared Drive. So, Please perform following tasks.
Step-1: You can see above image. Many time we use preview pane. When we use preview pane means your file is open. So, We can not save it when using from shared folder. This problem occurred in Email Copied.
Step-2: How to disable Preview pane?. First of all click on "View" menu and then click on Preview pane or Used short cut key "ALT+P".
Note: If You will want to more information, Please mail me on "info@itsolution4u.in"