Hi and welcome to LinuxQuestions,
It's most likely the conflict between the swfplayer and flashplayer as discussed in several threads here on LQ. Both cannot seem to work on the same system. Deleting the swf plugin should do the trick. In your address bar type:
and check if you have both the Shockwave flash player and the Adobe Flash player installed. Post the relevant information of those two here please. Also post what browser and version you're using.