Keynote error VRAM

He,

I'm having a annoying problem lately with one of my clients.

My client uses keynote for running presentations.

The presentations begins every morning and ends every evening, so its only not running at night.

After a while every mac shows the error: The computer doesn't have enough VRAM to play this presentation with this display resolution.

He uses old and new mac mini's al with 10.6.8

The weird thing is that keynote is the only applacation that is running.

I thought recently it could be solved when we upgraded to a new macmini with 10.7.2

It ran perfectly for a week till an hour ago.

It gave the same error again but this time with the newest mac mini en the newest software...

Keynote is also up-to-date.

Can someone help me?!

bye,

Remy

p.s.

I'm from holland so don't mind my grammer!