Getting started with Verilog and ModelSim

I'm trying to get started using Verilog and a student version of ModelSim. So naturally the first program I want to run is a simple "hello world". The code compiles fine, but for some reason I can't run a simulation. When I try to simulate, the $display line is highlighted in red (I'm guessing to indicate an error message of some sort). If it is an error, why does the code compile ok?

Thanks!