On Vista? You must use the latest Flash Player (9,0,28 or higher)
I just read an informative post on Justin's blog about how older versions of the Flash Player will not work as expected on Microsoft Vista due to changes in the security model. The areas that are reported as being affected are express install, shared objects, local connection and file reference.
Basically, in order for Flash content to play properly on Vista, users must run the latest Flash Player version (9,0,28 or higher).
In other words, if your users are on Vista and complain that your Flash sites or applications are not working properly, you'll have to tell them to upgrade to the latest player.
Thanks for the heads up, Justin!