I found this solution on StackOverFlow. If you ever run into this problem while running your meteor app :
"Can't listen on port 3000. Perhaps another Meteor is running?
Running two copies of Meteor in the same application directory will not work.
If something else is using port 3000, you can specify an alternative port with --port <port>."
Just run this command.
kill -9 `ps ax|grep node|grep meteor|awk '{print $1}'`
Then run 'meteor'command back.
