Whiteboard doesn't connect to 90% of my contacts. My firewall is configured (Windows Firewall) to allow RTC AppSharing (which also contains the whiteboard), I'm sure there's no problem with firewall as it at least works with some people.

But with most people; after clicking accept in MSN Messenger, the small box comes up it says Waiting for a few seconds and then Connecting... until the timeout error message. Does it have something to do with their firewall, which I can't ask as nearly all of them doesn't know what "firewall" means. But not that many people may have firewall, they know nothing about security.

It is absolutely not the connection speed too, if there's no problem it connects just in a second usually. I tried all while my bandwidth was free, so nothing to do with speed too, (they also have fast connection etc.)

What can be the reason then?

Sounds like it is their firewall. And you'll find that, even though many aren't aware, XP SP2 automatically enables the Windows Firewall, so they do have one.

But they would ask me if the firewall popup would appear (to block or unblock)