Client problems

I have postfix running together with qpopper as a mail-gateway. One client
always has to specifiy it´s password even if it is already saved on the
client machine. /var/log/mail tells me that perhaps another session would be
active and gives a hint to a file /var/mail/.<username>.pop. However, this
file doesn´t exist at all. How can I get rid of this problem. I am using
SuSE 9.0 pro.

Harry