There is a sticky post up above made about a year ago that acknowledges VC will not work if someone is dual-boxing on the same machine. VC would only allow one account per machine to be active.
It appears that many of the people posting here have routers, which would imply they have multiple computers running. Perhaps that is the heart of the issue. VC was not happy when multiple accounts ran on the same computer and now that VC is sitting outside EQ2 it is not happy with multiple computers logged onto the internet. That could be why VC works for some people when they play directly from their modem which would imply no conflict with multiple computers.
It may be time to relook at the dual-boxing issue which has apparently been ignored for the last year.