This is because you have some kind of Third party camera software installed like Google video chat, Manycam, Webcammax, etc. Uninstall these programs and then do the following:
1.Open Finder and select your main HD
2.Find the "Library" folder and enter it
3.Find the "Quicktime" folder and enter it
4.Delete any ".component" files that have to do with the programs listed above
5.Close and reopen your browser
6.Go to any minglcafe room and try to broadcast