Thank you very much, that was a big help. Would never have thought myself that it could be the quotes! I had another go at playing with them, and everything is fine now, I can finally start practising!
For campers who might have the same problem:
Apple menu -> System Preferences -> Keybord ->Text.
UNcheck “Use smart quotes and dashes”. Also, from the option list select the least fancy double and single quotes - in my list that was the last option in the list.