If you are using a USB webcam, make sure it is plugged in and working. If you have a built-in webcam, occasionally these may not be detected automatically.
Firstly, make sure there are no other video applications open, for example, Skype, FaceTime etc. These may be connected to your camera and stopping Tazio connecting.
Secondly, try using an alternative browser, Google Chrome and Firefox are both free to download and install.
Finally, try rebooting your computer which in most cases will fix the problem.