Dave Bowman's (well, sort of Dave Bowman's) last message was "All these worlds are yours except Europa. Attempt no landings there."

Humankind DID pay attention to the warning. After it was sent, we only sent probes into Europa's atmosphere, which were usually destroyed before they got close enough to the planet's surface to interfere with its life. Later, a spaceship had to make an emergency landing on Europa due to a crazy person with a gun taking over the ship, and the second and last intentional human landing on Europa was the rescue of that ship. The first was a Chinese expedition, in 2010. It was destroyed by one of Europa's unique fauna (or maybe flora).

The first writeup in here said something like "Sending this message guarantees that humans will try to land on Europa the first chance they get," which really sells short Clarke's depiction of humans in general as being mostly smart and reasonable.