This issue will never be solvedunless VF change their basic system.
I believe the probems are caused by a "transparent caching proxy" which VF use to intercept signals.
There is more about this on the VF NZ forum site.
Apparently there is a workaround by requesting a static IP, which does not route via the proxy, rather than the dynamic IP used as standard.
Unless you know a VF technician you are unlikely to get this change made, and the company will not admit to the cause of the problem.
Nice price but rubbish product. I have been offered free cancellation and refund of last month's payment
