[Dovecot] Authentication Failure

Probably a newbie question.... sorry.

Did a deluser a week or so ago, but didn't remove any of the users files. I re-enabled the user via useradd with the -u and set the uid the same as it was before. Now when I try and log the user into his mail via Thunderbird, /var/log/messages reports

dovecot(pam_unix)[17259]: authentication failure; logname= uid=0 euid=0 tty= ruser= rhost= user=sean

Any help is appreciated. Thanks.