TLS wrrors on cyrus imapd log file

[Riccardo Veraldi]

Hello,
I am using cyrus-imapd-2.4.10

I have configured it properly with X509 certificates.
Everything is working fine but for every client connection I receive 
this error: TLS server engine: cannot load CA data

Sep 16 04:04:42 iride imaps[9363]: TLS server engine: cannot load CA data
Sep 16 04:04:42 iride imaps[9363]: imapd:Loading hard-coded DH parameters
Sep 16 04:04:42 iride imaps[9363]: SSL_accept() incomplete -> wait
Sep 16 04:04:42 iride imaps[9363]: SSL_accept() succeeded -> done
Sep 16 04:04:42 iride imaps[9363]: starttls: TLSv1 with cipher 
DHE-RSA-AES256-SHA (256/256 bits reused) no authentication
Sep 16 04:04:42 iride imaps[9363]: login: wilco.mylocaldomain.org 
[172.16.10.94] username plain+TLS User logged in

X509 certificate is ok it is not expired; it complains about CA 
certificate data, but the certificate path inside imapd.conf is correct.

what the problem could be ?

thank you

Rick