Hi,
I could reproduce this issue and I think that I know why this error occurs with your file.
I have a suspicion that you are trying to import a F2C Article in the back-end. In the back-end you can only import Content Type definitions in the Content Type Manager.
F2C Articles can only be imported in the front-end. Please see the documentation:
http://documentation.form2content.com/f2c-xml-import-export/109-import-export-of-f2c-articles-data
The error message you receive is not good, I will see if I can find a way to give a proper error message to the user.
best,
Julien