Linux-PAM 1.1.8: failed to start pam transaction: 26

Dear list,

When I run weston-launch (wayland 1.2.1 and weston 1.2.2) as a normal user, member of the
weston-launch group, I obtain the following error message with linux-pam 1.1.8:

    failed to start pam transaction: 26: Critical error - immediate abort

I have installed linux-pam as a non-root user, my OS allows this.

Do you know where the error comes from?
What may I do to help find the origin of the problem?

Thanks,

Christophe