In the settings, you need to enable cellphone support (under System Configuration > Network Setup).
Configure the Windows Firewall to unblock the port you are using, by default the port is 5101. Or you can add the DVR program to the exceptions list.
If the PC DVR is connected to a router, you may need to open the port in the router as well.
It is recommended to create a new user with viewing-only rights, and login using this account from all mobile viewers since passwords are sent in clear text. You should enable network password support for that user.