>>> Emerging (1 of 1) media-video/mplayer-1.0_rc4_p20091124-r2 from gentoo-quebec
>>> Jobs: 0 of 1 complete, 1 running Load avg: 1.36, 1.52, 1.43
!!! A file listed in the Manifest could not be found: /var/lib/layman/gentoo-quebec/media-video/mplayer/mplayer-1.0_rc4_p20100328.ebuild
>>> Failed to emerge media-video/mplayer-1.0_rc4_p20091124-r2
You have to find the people who are responsible for this overlay and report it to them. I gave a try on irc but noone was around at that time. Maybe you could open a thread on their forum --> http://www.gentoo-quebec.org/forum . This is not an official gentoo overlay, I will resolve this bug as CANTFIX. Thank you for your report.
(be aware that there are newer(unstable) mplayer versions in the main portage tree)