Matlab 2014 Simulink stupid connector errors

You start Matlab, start Simulink, and the moment you run any simulation you get a big pile of shit similar to this:

Error using connectorHandler>performAction (line 77)
Error starting MATLAB Connector. Please check that port 31515 is available.
 Error in connectorHandler (line 32)
   Error in connector (line 14)
    [isRunning, hostInfo] = connectorHandler(action, varargin{:});
 Error in connector.ensureServiceOn (line 22)
   Error in slmsgviewer (line 58)
   Error in slmsgviewer/PersistentInstance (line 304)
   Error in slmsgviewer.processRecord (line 404)
  
Error using connectorHandler>performAction (line 77)
Error starting MATLAB Connector. Please check that port 31515 is available.
 Error in connectorHandler (line 32)
   Error in connector (line 14)
    [isRunning, hostInfo] = connectorHandler(action, varargin{:});
 Error in connector.ensureServiceOn (line 22)
   Error in slmsgviewer (line 58)
   Error in slmsgviewer/PersistentInstance (line 304)
   Error in slmsgviewer.processRecord (line 407)
  
Error using connectorHandler>performAction (line 77)
Error starting MATLAB Connector. Please check that port 31515 is available.
 Error in connectorHandler (line 32)
   Error in connector (line 14)
    [isRunning, hostInfo] = connectorHandler(action, varargin{:});
 Error in connector.ensureServiceOn (line 22)
   Error in slmsgviewer (line 58)
   Error in slmsgviewer/PersistentInstance (line 304)
   Error in slmsgviewer.processRecord (line 404)

This happened to me running Matlab 2014a, but probably it's the same for older and newer versions. 

The people of the internet only spoke unhelpful bullshit about Java versions, so I had to take this seriously and work this out by myself.

If you have a firewall stopping Matlab's network connection (which I had, considering my copy is pirated) then that's your problem. Matlab needs the internet to work without complaining, for reasons no one here cares. So, create a rule or disable your firewall while using it and there you go. As far as I know, there's no mess with the activation.

Also, as far as I tested, I believe that Simulink works properly despite of the errors.