You can check for Internet Plugins which may be competing for video control and causing an error. The common locations would be ~/Library/Internet Plug-ins and /Library/Internet Plug-ins.
You can access those locations by being in Finder and selecting Go > Connect to Folder, and typing in the above folder file paths.
Try removing these one at a time, restart and test if issue is resolved.
http://support.apple.com/kb/TS3230 has additional troubleshooting suggestions.