Success!

Well, that sorted out a problem which has taken me well over an hour. Still, I triumph over modern technology which doesn't happen very often :)

So, if like me you've fallen foul of IE9 this is how I solved the problem:
1. Go into Settings
2. Scroll down to Global Settings
3. Select post editor
4. Click on 'Updated editor (recommended)'
5. Click on 'Save settings'
6. Try posting.

Good luck :)