From the Tool website:

"Tool has CANCELED Wednesday's appearance at the FREQUENCY FESTIVAL IN SALZBURG, AUSTRIA due to illness. Maynard has contracted a really bad throat infection which he has been fighting for the past couple of days, but, unfortunately, it has now reached the point where the band has to cancel."

Noooooooooooooooo! Please get well soon MJK before Sunday, I am really looking forward to another Tool show!

Update: They didn't cancel for Lowlands and played a great set. Didn't notice any problems with his voice.