Score won't save online

I'm working on a transcription of the overture from the Nutcracker Suite and when I try to save it, I keep getting an error message that says

"Your score could not be saved to the cloud

MuseScore.com returned an error code: 401 Authorization required.

Please try again later, or get help for this problem on musescore.org."

I'm saving to the cloud because my computer is running out of space.
What could the problem be? Why can't I save my work? Any help is greatly appreciated