I have a silverstripe install thats working perfectly except for one thing...

When I visit a page with a type 'userform' I always get a blank page.
If I am logged in as admin then page shows fine on the front end. It's only when logged out and viewing as a guest that this page is blank.

I have the site in dev mode but there is no trace and nothing in the log file.... very very weird.

I've tried various releases of userforms including a few trunk builds but keep getting the same thing happen.

Does anyone have a clue what might be happening here or how to troubleshoot this further? I'd happily pay a few quid to get this sorted out because our site is unusable useless to visitors with contact forms to get in touch.