mezzanine field injection failing

edit

Following my work with mezzanine, I'm trying to inject a field by:

1>> Adding the EXTRA_MODEL_FIELDS in settings.py pastebin.com/d5amC7fj and then

2>> Creating the file admin.py pastebin.com/zstJNCma under my 'customizations' application.

But when I try the schemamigration, I'm getting an error I can't understand at all pastebin.com/exLtcQSs.

What am I missing here?

Any and all comments are welcome.

Thanks a lot in advanced!