[DCP-o-matic] mp4 issue?

Hi Carl - I just downloaded your DCP-o-matic! I am trying to convert a mp4 file to a DCP file, but I am not allowed to start with my MP4 as you can see from the attached screenshot. I have looked in the tutorials, forums, FAQs, etc. and can't find this specific issue. Can you please help me? I am not the most tech-savvy person on the planet but I am pretty sure I can figure this out if I can just get my file imported! I'd also like to be added to the mailing list. Thank you so much, Kelly Marshall