There are no graphics card drivers installed on his computer. The client automatically switches to software rendering (classic client). He can still play, but not with the improved graphics. To resolve that, he must install a graphics card driver.

''HE CAN STILL PLAY''
He cant, if he clicks on OK
It goes away

Hmm... that shouldn't happen. Alternatively, he can also change the game to software renderer at the setting of the loader (bottom right). I highly recommend not to play on the software renderer though and install appropriate graphics card drivers to run emps.