Why is there a blackoutline when mouse put over Flash movie?

I have developed some Flash work.
All is fine.
Except one user get a black outline in their browser whenever the mouse is put over the Flash movie.
I have 3 Flash movies. The same occurs for each of them.
I can’t figure out why this is happening.

Is this an accesibility feature?

It only happens on one computer.
All other are fine.
The use is using Internet Explorer.

Also, the Flash movie is developed in Flash 8, but published as a Flash 6 movie.

Any help would be appreciated.

Thanks.

OM