weston-launch: "fatal: failed to create compositor"

[christophe.jarry at ouvaton.org]

Hello,

I have built Wayland according to the instructions available on
http://wayland.freedesktop.org/building.html. Then, as a normal user (member of the group
weston-launch), I do:

    weston-launch

I obtain these errors:

[18:26:39.128] couldn't open /dev/dri/card0, skipping
[18:26:39.128] failed to initialize kms
[18:26:39.128] failed to drop master: Permission denied
[18:26:39.280] fatal: failed to create compositor

What is the problem and how may I fix it?

Thanks,

Christophe