This problem is caused by a security setting in ventrilo, it will block poeple trying to connect from the same ip.
The number of users allowed to connect under the same IP can be changed inside the ventrilo server.
- Connect to the ventrilo server (How to connect to your server).
- Loggin as administrator (How to login as server admin).
- Right click in the white area of the ventrilo to open the menu, go in "Server Admin" -> User Editor
- Click the user in the userlist on the left. Then click the network tab and select duplicate IPs unlimited then click update.