Claudio Pasolini,
"CA certificate file is not readable or does not exist"
is the clue.
Verify that the cert files are located in the ModuleDir. You might want to try using an absolute path to each cert file, for example:
ns_param CertFile /var/lib/aolserver/service0/etc/certs/certfile.pem
Verify that the cert files have any password removed. See the nsopenssl README file for instructions.
Verify permissions for these files.
Also, note that (apparently) openssl has a limitation that prevents more than one server (at least using nsopenssl) from using the same cert files. So, create a set of cert files for each server used. Copies should be okay.
hope this helps,
Torben