NetBSD 3.1, vsftpd with virtual users

Hello
Ive got an issue with Virtual Users on vsftpd.
I installed packages vsftpd, PAM-0.77bn5 & pam-dbm-0.2nb1.tgz.
When I try to connect with the login "toto" and password "tata" -registered in a
"vsftpd_login.db" file (generated with berkeley db) and pointing on the user
"virtual"- I have an error message :

PAM-warn[xxx]: function=[pam_sm_authenticate] service=[vsftpd]
terminal=[<unknown>] user=[toto] ruser=[<unknown>] rhost=[<unknown>]
530 login incorrect.

I don't understand this message, so I could not find the origin of this problem!
thanks in advance,
romain matuszak
France