On putting in a tape the machine would indication "PLEASE RE-OPERATE AFTER PUSHING RESET BUTTON".
After locating the reset button - which is s tiny screw next to the Eject button which needs to be pushed using a pin or something small - it would reset and indicate "TO SERVICE".
After looking on-line I found this blog which had the answer:
By removing the cassette and curling my little finger onto the play head (the silver drum at the bottom of the compartment) from below, I gently nudged the play head (a silver strip on the drum) back and forward.
Putting in the cassette again - and the problem went away. It seems that the play head had got stuck and needed to be rotated a little to get it back into action.