cyrus imapd and db3 lock file

[RJ45]

Hello,
It happens to me that I had 480 processes of imapd running on my mail
servers, people could not access to INBOX and I had thousand messages
like these:

Jan  8 06:06:14 postino lmtpd[12648]: DBERROR db3: 157 lockers
Jan  8 06:58:19 postino lmtpd[13020]: DBERROR db3: 158 lockers
Jan  8 07:50:47 postino lmtpd[13622]: DBERROR db3: 159 lockers
Jan  8 08:05:48 postino pop3d[13919]: DBERROR db3: 160 lockers
Jan  8 08:21:52 postino imapd[14138]: DBERROR db3: 161 lockers
Jan  8 08:22:53 postino imapd[14140]: DBERROR db3: 162 lockers
Jan  8 08:23:37 postino imapd[14123]: DBERROR db3: 163 lockers
Jan  8 08:23:53 postino imapd[14156]: DBERROR db3: 164 lockers
Jan  8 08:24:54 postino imapd[14184]: DBERROR db3: 165 lockers
Jan  8 08:25:54 postino imapd[14211]: DBERROR db3: 166 lockers

what could be cause this?
I never had this problem before with cyrus.
I have FreeBSD 4.6

thank you for any hints u can give me.

Rick