OK so playing with permissions etc didn't work at all.
So I uninstalled it all and started again...twice.
On the third time, after copying all the Limesurvey files on to the server it didn't work still. So this time, without deleting anything, I copied the same set of files over the top of those I'd already uploaded.
Hey presto, all working as it should.
I have no idea why when I used the same set of Limesurvey files from the outset. But this time bingo. Happy days.
huge thanks to you all who gave help and advice - I really appreciate this.