`drush fullcalendar-plugin` returns error

I just downloaded the latest version of fullcalendar dev. (I also tried the latest recommended with the same results). It returns Drush was unable to download the FullCalendar plugin to sites/all/libraries.

Nothing looks out of place in that folder. Permissions are 777 for debugging. There isn't already a fullcalendar folder there.

Any ideas what else I should be checking? I'm running Mac osx.