[CentOS] DBERROR db4: Logging region out of memory;

Hi Folks,

I have problems with delivering of mails.

In /var/log/maillog are these error messages

Mar  3 16:00:42 server pop3[15665]: DBERROR db4: Logging region out of memory; 
you may need to increase its size

Mar  3 16:00:42 server pop3[15665]: DBERROR: 
opening /var/lib/imap/tls_sessions.db: Cannot allocate memory

Mar  3 16:00:42 server pop3[15665]: DBERROR: 
opening /var/lib/imap/tls_sessions.db: cyrusdb error

unable to get certificate from '/etc/pki/cyrus-imapd/cyrus-imapd.pem'

Mar  3 16:00:42 server pop3[15665]: TLS server engine: cannot load cert/key 
data

Mar  3 16:00:42 server pop3[15665]: [pop3d] error initializing TLS

Sorry, I'm not skilled so much - please give me some hints.

System: CentOS 5.0

Thx
Timothy