Drupal installation

I am unable to add content to my Drupal installation. When I follow the instructions on the page http://h5p.org/node/591#guides-header-1 (3. Test that it works.), I get the following error:
The specified file 616.zip could not be uploaded. Only files with the following extensions are allowed: h5p.

Any clue? Do you need more information?

Thanks!

Where did you get 616.zip from? Did you download it from h5p.org using Internet Explorer? Try changing the file ending to .h5p and upload it again.