config problem : CreateObject('emailadmin.bo'): Cant instanciate class!!!

I can't go further in installing EG 1.4.002 under debian lenny : when I try
to fill the setup/config.php page where one can fill the email servers informations,
I always get a page saying :
"CreateObject('emailadmin.bo'): Cant instanciate class!!!
mail_server(Array)"

Apache2 is up and running on my box, with php5-imap installed (everything, including egroupware-*, was
installed with apt-get)

any idea ?
help very appreciated, I can't go far away !