Using Prism 4 Mac under OSX, when I try to dupicate a graph with its data sheet (duplicate with family ), Prism shows an error message "this file is in use or read-only".

 This bug is intermittent, but the programmers were able to find it and fix it. This was fixed in 4.0b.

The workaround for now is to save the project, close the project and open it again. That often makes the problem go away. It may also help to not enter a prefix (for new sheet names).