Well that error is a Ventrilo error saying it can't talk to your hardware to use it. Open setup and see what Vent has been set to use for your Input device. Once noted look in Control Panel\Sound\Recording and see if the same device is listed.
If it is not, right click where the recording devices are/should be listed and enable show disabled/disconnected devices. If the one you are looking for is there, see if you can enable it.
If you still don't see it there but see other devices listed go back to the Input selection for Vent and see if those are in there, select one and see if it works.
Also you can select codecs in the setup window for vent. They're in the bottom left corner, in the Test section. I saw a GSM 6.10 listed in there.
Hope this is of some help and good luck
