Adding score on behalf of a composer

[OE1FEU]

I have been asked by a composer to create a new entry for a work of his, which worked fine. I have then tried to add the score, which is a PDF from the manuscript, which did NOT work.

I thought I had the necessary stepd followed correctly:

* Add file
* Add sheet music
* Upload File
* Add to tab "Scores"
* Fill in the details, specifically: File/Image Type: Manuscript Scans
* Choose License CC, perf. and deriv (Last entry, just like his previous works
* Publisher: Name of the composer (Frederic Rzewski)

As soon as I try to finish this, I get this error message: "Scans must be public domain. If you composed the music yourself, or have permission from the composer, select 'New Compositions' instead. Please visit this page for more information."

This is where I am lot. I am not the composer, but acting on his behalf, and I haven't figured out that yet and the error message is not helpful. Can someone please explain to me how to upload an original composer's manuscript when I am not that composer myself?

I have searched the forum and read all the relevant documentation, but never found any hint regarding "New Compositions".

Thanks for your help.