The message means that the port is in use by another application.
Description of all the ports used by PC-CCTV is given in the Section "Network". If port number is not important (see below), then simply change used ports in the section "Network".
However if DVR requires fixed, specific list of ports and some of them are in use by another application, then you will see message "Error. Port XXX is occupied by another application! Display information about this application?", press "Yes" and see which application uses the port.
When you found out which application use the port you need, read how to change port in the manual of the application, or see help in the Forum