Remote PC's will not inventory or pull policy unless connected via VPN

Hope someone can help with this.

We are running LDMS 9 SP2 and have noticed that none of our clients will inventory or pull policy when outside of the corporate network unless they are connected to VPN.  When i try to run a manual inv scan we get the error ldiscn32: failed to resolve host name.  We cannot obtain a client certificate via brokerconfig.exe unless we are connected to VPN and when we try to use desktop manager we get the same result.

Any help is much appreciated.

thanks

Eric Scott