Problem solved: WordTube 2.0.0 and WordPress 2.6.2

Go to http://www.jeroenwijering.com/?item=JW_FLV_Media_Player and download the JW FLV Media Player 4.1.

Unpack the content and upload player.swf and yt.swf to the wordtube plugin folder.

This doesn't fucking work with automatic plugin update so you gots to do it manually.