I've had this issue for a while, but it only occurs on my iMac and it only occurs on "some" Flash sites. It happens in both Safari and Chrome and has continued over multiple browser and Flash versions. I'm running the latest and greatest version of Lion (fully patched as of 4/13/12), but this has been occurring for quite a while through multiple versions of OSX, Flash, Chrome and Safari. I've also tried running "Repair Disk Permissions" and that doesn't fix the problem. When I check Adobe.com/software/flash/about in Safari, it tells me that I have "184.108.40.206" installed. When I check using Chrome, it tells me that I have "220.127.116.11" installed. Videos on Youtube, Mevio, Vimeo, DailyMotion and others play just fine. However sites like South Park Studios and Funny Or Die do not play and just show a black box where the video should be playing (the Flash banner ads display just fine). My MacBook Air is running all the same OS and software versions, but has not had any problems with these sites. Does anyone have any ideas on how I might fix this problem on my iMac?