[Dovecot] Timeout while waiting for release of fcntl() lock for mbox file /var/mail/mailbox

Hi there, im currently using dovecot 0.99.11 (dovecot-0.99.11-4.EL4) on Centos 4.4 i386

/var/log/maillog has started to produce several times per minute this entry: Mar 9 14:52:44 mail pop3(albrook): Timeout while waiting for release of fcntl() lock for mbox file /var/mail/albrook

when this happens, users cannot receive email properly, but eventually (maybe a few minutes or a few hours) the email gets delivered.

is this a problem in the 0.99 version? can i safely upgrade to 1.2?

thanks,