There are a few conditions that might prevent you from using UnoDNS:

1. If your Internet Service Provider does DNS filtering/censoring (Perform a Free OpenDNS test to check this) 

2. If your network is restricted such as in a hotel

3. If you are using 3G/4G network
4. If you are using Public Wi-Fi 

5. If you are using Satellite Internet. (This works for some people, but not for most.) 

You can perform an OpenDNS test to verify if our UnoDNS services will work for you or you can sign up for a free trial and try it out!