Viso 2013 blank shapes

[anna]

Hi all,

I have some Visio files that were created in Visio 2007, in which I used shapes that were self-created (not by me).
Now after installing Visio 2013, when I open these files (or even try to create new diagrams with that shape stencil) I see blank rectangles with a cross over them.
On the Shapes sidebar I can see the shapes I want to use as they should be, but when I drag and drop them on the page they turn blank.

How can I solve this problem?

Thanks.