@mitu That's actually an excellent question.
I have been using my own launcher which only has the command 'emulationstation' -This was the error. If I run the command in a terminal window or use the rpie launcher which does the same; Everything works. So a massive thanks to you!
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first