It's 10.15 on Sunday morning and after playing with this for 24 hours, I give up!
I got the theme and tried the perimeter as per the instructions. Like a number of other posters, I realised this must be wrong because of the two 3 letter clues on the perimeter. So following a hint on this site, I started at the top right and it seemed to work ok. I have both the 10 letter answers but which ever way I put them in, I reach an impasse.
There must be better ways to spend the weekend.