This error message is what Voicent software gets from your VOIP service. The following are some of the errors:
Your VOIP service is temporarily not available
Your VOIP account does not have enough calling credit
Your VOIP account does not have a correct calling plan (such as Callcentric cannot call regular phone if you have "IP freedom" plan)
Some of the errors like "480 Temporarily Unavailable" or "408 Service Timeout" are caused by bad telephone numbers. To verify, simply call the phone number manually
All these errors are not caused by Voicent software. You must contact your VOIP service provider for more information.