mediawiki - 403 forbidden

[Roger Searle]

Hi, following my version upgrade to Hardy Heron my installation of 
mediawiki is broked giving me

Forbidden
You don't have permission to access /mediawiki1.9/index.php/Main_Page on 
this server.

My googling just shows up how little I know about apache and mediawiki - 
it was quite a bit of luck that I got it running in the first place.  
While looking through some installation guides I'm guessing it needs to 
be reconfigured but have no idea where to start.  Any pointers would be 
gratefully received and studied.

Cheers,
Roger