What Flex applications are you running when you get this
error. Were they old Flex 2 applications compiled with a previous
Beta or Alpha? This looks like the error you get when you load a
Flex app that is not compatilble with the player.
When you installed Flex 2, you probably installed the new
player. You will need to recompile your old apps with your new
build of Flex 2.
Flex 1.5 apps should all work fine in the latest Flash 9