Disappearing Emails

Exchange server 5.5 and clients running Outlook 2000 with their mail stored on server. One of our users is not getting mail intermittently. Earlier today an email was sent to her, I saw it in Event Viewer as Event ID 2002 said “A message from in temporary file D:\location of imcdata\in\KQ63J3F1 was received from incoming.domainname.com with 1 local recipients”. Then Event ID 2000 showed up with “A new TCP/IP SMTP event has been received from host incoming.domainname.com Log File: L0000000.LOG.” The user never received this mail. It’s like it made it to exchange but not to their desktop. Any suggestions? Please help, of course this is only happening to the bosses PC! (from what I can see). Thanks!