'You need flash player installed to preview ppt and pdf files' message persists after flash is installed in IE9

The message, as well as a link to the adobe website from which you can install Flash is still displayed after Flash is installed, underneath the pdf that is being rendered by the viewpdf macro.

The following is a screenshot given to us by a client experiencing the problem.

A possible reason for it can be that The flash plugin has a different name (Shockwave Flash Object) in IE9 than it does in Firefox (Shockwave Flash).