Strange logon error

[Patrick NG Kwok-fai]

I have encountered a strange logon error and hope you can give me some
light. I  logon imp server using logon name andrew, it is working fine.
However, if I logon imp server using logon name peter, the logon will be
failed.

I have found some error in /var/log/messages

Jul 26 15:18:56 co imapd[23242]: login: localhost[127.0.0.1] andrew CRAM-MD5
Use
r logged in
Jul 26 15:19:48 co imapd[23242]: login: localhost[127.0.0.1] andrew CRAM-MD5
Use
r logged in
Jul 26 15:43:25 co imapd[23310]: badlogin: xx.xx.com[20x.8x.5x.24x] CRAM-MD5
authentication failure [no secret in database]
Jul 26 15:43:31 co last message repeated 2 times

The imp and horde installation is resided on the public_html directory of
andrew. I don't know the error is due to such configuration or just CRAM-MD5
issue. Would you be kind helping me to solve this problem? Thanks

Sincerely,

Patrick NG