Please help - Not authorized errors on every form submission.

I've been doing a lot of work on forms on my site. Suddenly, every time I try to submit a form, ANY FORM, and that includes things like clearing the cache and changing permissions - I get "You are not authorized to view this page." This is on the first account so, I am effectively locked out of my site. I can see everything, but I can't DO anything.

I'm in serious need of help here. If anyone has an idea I would be very grateful.

Thanks.

MK