The numbered buttons don't seem to work when I'm running SC on either my LinkStation HG or the LinkStation Pro I am testing for a friend. Both of them are debian-based machines with build 20910 built from the tarball. When I run it off an Ubuntu server also running 20910 (installed via dpkg) the buttons worked just fine. 

Michael H suggested a permissions problem with favorites.opml in the playlists and/or cache directories, but the permissions on the LinkStations are either the same or less restrictive than those on the Ubuntu box that works. Ownership is squeezecenter:nogroup on all of them. I tried changing the playlist and cache folders on the LS Pro to 777, and the favorites.opml and favorites.opml.backup files to 666, and I still get the same errors.

Here are some of the error messages in the LS Pro server.log:

[08-06-19 17:01:18.8466] Slim::Control::Request::execute (1781) Error: While trying to run function coderef [Slim::Control::Commands::buttonCommand]: [Can't locate object method "hasHotkey" via package "Slim::Plugin::Favorites::OpmlFavorites" at /usr/share/squeezecenter/Slim/Buttons/Common.pm line 825.
]
[08-06-19 17:01:51.4366] Slim::Control::Request::execute (1781) Error: While trying to run function coderef [Slim::Control::Commands::buttonCommand]: [Can't locate object method "hasHotkey" via package "Slim::Plugin::Favorites::OpmlFavorites" at /usr/share/squeezecenter/Slim/Buttons/Common.pm line 825.
]
[08-06-19 17:01:58.4717] Slim::Control::Request::execute (1781) Error: While trying to run function coderef [Slim::Control::Commands::buttonCommand]: [Can't locate object method "hasHotkey" via package "Slim::Plugin::Favorites::OpmlFavorites" at /usr/share/squeezecenter/Slim/Plugin/Favorites/Plugin.pm line 168.
]
[08-06-19 17:02:00.7048] Slim::Control::Request::execute (1781) Error: While trying to run function coderef [Slim::Control::Commands::buttonCommand]: [Can't locate object method "hasHotkey" via package "Slim::Plugin::Favorites::OpmlFavorites" at /usr/share/squeezecenter/Slim/Plugin/Favorites/Plugin.pm line 168.
]
[08-06-19 17:02:01.7746] Slim::Control::Request::execute (1781) Error: While trying to run function coderef [Slim::Control::Commands::buttonCommand]: [Can't locate object method "hasHotkey" via package "Slim::Plugin::Favorites::OpmlFavorites" at /usr/share/squeezecenter/Slim/Plugin/Favorites/Plugin.pm line 168.
]
[08-06-19 17:02:03.0114] Slim::Control::Request::execute (1781) Error: While trying to run function coderef [Slim::Control::Commands::buttonCommand]: [Can't locate object method "hasHotkey" via package "Slim::Plugin::Favorites::OpmlFavorites" at /usr/share/squeezecenter/Slim/Plugin/Favorites/Plugin.pm line 168.
]