Some users can't view my streams

I've got live streams up on my website (using FMS3), but very occasionally, I'll get a complaint that someone can't view the streams. The swf player is loading, but the stream is not. The user updated to the latest Flash player and still no luck.

My first thought is that they have a firewall blocking RTMP requests. So today I mucked around and got the HTTP tunnelling going (RTMPT), hoping it would resolve the issue. Well it didn't, same results, even over port 80. So I guess I have a couple of questions:

1) Does anyone know of a non-firewall-related reason that users (at least 2 different users in 2 different locations) might not be able to view RTMP or RTMPT streams?

2) Does anyone know how I can troubleshoot this further?

3) Does anyone have any sample streams (running on FMS3, preferably live streams) I can point the troubled users to in order to test if it is ALL streams or just the ones from MY server?

4) Can you guys test my streams and tell me if you can't see them?

http://www.ashevillelivecam.com/asheville/north.html
http://www.ashevillelivecam.com/asheville/south.html
http://www.ashevillelivecam.com/asheville/east.html
http://www.ashevillelivecam.com/asheville/west.html


Thanks for your help.