[Dovecot] 1 user has random pam auth issues

Hi

Dovecot 1.0 stable on FC3

i see this in my logs from 1 user

Oct 19 07:20:36 proteus2a dovecot(pam_unix)[2937]: authentication failure; logname= uid=0 euid=0 tty= ruser= rhost=1.2.3.4 user=testuser

IP & user changed by me.

at other times he has no issues. no other users are reporting this. could it be his ADSL is flaky or is there another scenario.

Mark