Bellow is a list of common reasons why video will buffer/freeze and some troubleshooting tips:
1) Your internet connection is weak or unstable. Try testing this by loading up another site like http://google.com and see if you experience any connection issues. If you are unable to connect to another site try resetting your wireless router or restarting your computer. If the internet connection is still unstable try contacting your internet service provider (ISP) for further assistance.
2) There are too many other programs running. Close down all other programs to ensure they are not interfering with your video upload. Any program that might be using your network's resources could cause a problem. Things like YouTube, Vimeo, or streaming radio are good examples of this.
If the troubleshooting tips above do not resolve your issue please contact Customer Support for further assistance.