If you choose the top level Permissions and then select any permission from the right pane "All Permissions" view.  You get the error displayed below, I also got the same error running form the RBS Sample.

Exception
  Could not create permission editor.

Source     : MicroFour StrataFrame Security

Stack Trace:
   at MicroFour.StrataFrame.Security.SecurityDialog.CreatePermissionForm(Int32 ProjectPK, Int32 ItemPK, String Category, Boolean IsCopy)
   at MicroFour.StrataFrame.Security.SecurityDialog.EditPermission()
   at MicroFour.StrataFrame.Security.SecurityDialog.lvDetail_DoubleClick(Object sender, EventArgs e)
   at System.Windows.Forms.Control.OnDoubleClick(EventArgs e)
   at System.Windows.Forms.ListView.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativewindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativewindow.WndProc(Message& m)
   at System.Windows.Forms.Nativewindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

I have just run the sample over here to check it, and it does show the error, but only if I "double click" the permission, which is the action to Edit it. If I only click on it, it just gets selected. And as you already know, Permissions are not supposed to be edited at runtime.