Well, if your Akai works in Reaper no problem, you've already eliminated it as the problem. Sounds like an improper setting in S1. Maybe you accidentally changed some setting? Anyways, here's a good tutorial that may be of some help:

https://www.youtube.com/watch?v=Wi2Kj8MX7_c

That being said we can help you better now and in the future with a bit more info......if you will post your system specs in your signature, (see my sig), we will be better able to troubleshoot your problems. Without knowing what type of pc you're running, what OS you're using, make and model of your audio interface etc....we often can't recommend a "simple fix"

If you have not already done so please READ THE MANUAL!

Thanks for your reply- I have watched the video and read the manual but still no joy, although the MIDI monitor shows incoming activity when I play the keyboard but still doesn't "play" the Virtual Instrument (even though the keyboard is selected in yellow on the focus device). As you said, it seems that another setting has changed though for the life of me I can't see what?

Hope you have some more ideas please?

BTW I updated my profile as well

I would contact Support about this. It may not be a complicated fix.

Thanks will contact them