This error was caused when I tried to locally run a server on a port that was already being used by another server that I had previously left running and forgot to turn off.
This command will show you all the process(es) running on a port and their PIDs
sudo lsof -i :3000
Kill the process by replacing <PID> with the process’ PID number
kill -9 <PID>
Joshua Bowen's Notes 