My experience has been that when the network is blocking or not allowing the video chat, the error message will make specific reference to the fact. I tend to doubt that is the problem.
If you haven't seen it yet, take a look at the following.
KB26096-Troubleshooting Wi-Fi and networking on the BlackBerry PlayBook
That isn't specific to the video chat app, but it should help with troubleshooting the wifi connection. That is where I would start. See what others say.
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