The MX61 was released after Cubase 5, so you may not be able to use the remote script from it. If you go to the Plus (+) symbol at the top left, do you see the Yamaha MX (or KX) as an option for the remote? If so, select it, set your MIDI in/out for it, and you should be all set.
If you do not see it (and you have installed the latest MX drivers), I would suggest using Generic Remote. If that is the case I would highly recommend checking out the manual on Remote Devices and Generic Remote because it will explain how to setup the desired parameters.
I hope this information is helpful. Please let me know if you still have trouble and I will do my best to help!