Javier,
I just checked to see if the Free Form Window works in AC 12
and it does. It also works in AC 10. I do not have AC 11 loaded
so I don't know if there is a problem in AC 11. Generally, objects
saved in an earlier version work in later versions so try it and see.
You need to check the materials, line types settings, etc
because between versions they may have changed.
Peter Devlin