[Dovecot] LF not found where expected

[Miles Mawyer]

I'm using Dovecot 0.99.13 on a fedora core 3 server. 
I keep getting these errors from time to time.
There user ends up retrieving no mail (but no error in their client, be it web mail or pop3 client)
What usually fixes it is this procedure:
Cp mbox file to mbox_
Remove original mbox
Send a test message to recreate mbox.
Cat mbox_ >> mbox
Problem solved!

Can anybody tell me what causes this?

 pop3(mjmurray): Jun 27 11:16:38 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected
pop3(mjmurray): Jun 27 11:16:38 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected
pop3(mjmurray): Jun 27 11:16:38 Error: Couldn't open INBOX: Internal error occured. Refer to server log for more information. [2005-06-27 11:16:38]
pop3-login: Jun 27 11:17:06 Info: Login: mjmurray [64.203.167.125]
pop3(mjmurray): Jun 27 11:17:06 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected
pop3(mjmurray): Jun 27 11:17:06 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected
pop3(mjmurray): Jun 27 11:17:06 Error: Couldn't open INBOX: Internal error occured. Refer to server log for more information. [2005-06-27 11:17:06]
imap-login: Jun 27 11:17:28 Info: Login: mjmurray [127.0.0.1]
imap(mjmurray): Jun 27 11:17:28 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected
imap(mjmurray): Jun 27 11:17:28 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected
imap-login: Jun 27 11:19:12 Info: Login: mjmurray [127.0.0.1]
imap(mjmurray): Jun 27 11:19:12 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected
imap(mjmurray): Jun 27 11:19:12 Error: Error indexing mbox file /var/mail/mjmurray: LF not found where expected


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