In my kamailio configuration, I already have &quot;#!define WITH_TLS&quot;. And some more about my configuration:<br><br><div style="margin-left:40px">listen=tls:XX.XX.XXX.XX:5061<br><br>#!ifdef WITH_TLS<br>enable_tls=yes<br>

#!endif<br><br>#!ifdef WITH_TLS<br>loadmodule &quot;tls.so&quot;<br>#!endif<br><br>#!ifdef WITH_TLS<br># ----- tls params -----<br>modparam(&quot;tls&quot;, &quot;config&quot;, &quot;/usr/local/kamailio-3.3/etc/kamailio/tls.cfg&quot;)<br>

#!endif<br><br></div>And my tls.cfg is,<br><br><div style="margin-left:40px">[server:default]<br>method = SSLv23<br>verify_certificate = no<br>require_certificate = no<br>private_key = /usr/local/kamailio-3.3/etc/kamailio/kamailio.key<br>

certificate = /usr/local/kamailio-3.3/etc/kamailio/kamailio.pem<br><br>[client:default]<br>verify_certificate = yes<br>require_certificate = yes<br></div><br>I
 have just installed kamailio 3.2.4 on some other server to see whether 
the problem is with my configuration/my system or with kamailio release.
 I again installed Ubuntu, and I installed the requested packages via 
apt-get, as I had done on problematic system. I used exactly the same 
configuration file, except changing the domain/ip values. And it worked.
 Then I used the same configuration file on some other versions of 
Ubuntu server, and it worked again. So, it really seems as a bug in 
kamailio.<br>
<br>It seems the worker children cannot be forked for some reason at 
startup, so I enabled WITH_DEBUG directive and restarted the kamailio. 
The output is attached to this mail. I hope it helps.<br><br>Best,