All works fine now - well almost. I get a javascript error message whenever the page with the quick search box for guests loads.
There's loads of Javascript in vb now (and I'm no expert) so I'm tempted just to leave it - I just hate seeing that little yellow triangle in the status bar though.
But guests can now post. I intend to remove guest posting eventually anyway - so maybe this is another way to get them to register. The promise of an "error free" board. They'll love that
I should add that I did add a hidden username field in the QRB.