The assert error is fixed on trunk but it's not related to not converting files, just the widget that shows disc usage. This looks like a dup of Bug #22501.
-- "Cannot Convert Files" (mp3) that Totem-gstreamer can play https://launchpad.net/bugs/37148 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs