Thank you very much for your attention and your answer.
I ran the 2 CVE cron scripts correctly. First the cron_all_software.php and cron_cve.php according to manual at wiki ocs and enabled verbose mode in OCS's GUI. I revised all the settings and realized that the problem was with the cve-search configuration. I could not access the server IP on port 5000.
I adjusted the configuration in cve-search: <<install_dir>>/etc/configuration.ini
and in OCS (VULN_CVESEARCH_HOST) as you informed and then the communication between OCS and CVESearch server which is configured locally worked.
Now I found another problem. I have nine OCS servers as slaves and one as master. All slaves communicate with CVESearch server and process the vulnerabilities but the master is not working. I revised all the settings on the master, they are the same as the slaves settings but it doesn't work. What could it be this time? Can you help me again?
Once again thank you very much, as your answer helped a lot to solve the first problem.