Client's machine won't play movie

I embedded a Flash animation. Plays fine on my and my boss’s machine. Our
client can’t play it. We converted it to a .wmv and re-inserted as link.
Still wouldn’t play. In both cases, he gets an error message: “Some controls
on this presentation can not be accessed. They may not be activated on this
computer.�

He went to the Help section. It said he needed to register custom control.
He tried. No go. It said he needed a Visual Basic control file and it could
not be found on his computer.

I’ve had this problem very occasionally with other clients. Never found an
answer and the problem is usually fixed by switching to a different machine.
However that’s not an option with this client.

Does anyone know how I can advise him to fix this problem, which is now my
very big problem?

Many thanks in advance