Cannot edit pages

Hi – I’ve searched this forum for similar topics, and have performed all (most) of the troubleshooting tips – deactivate/activate plug-ins, update plug-ins, update WP, update my theme…nothing seems to be working.

I can add a page, and update that new page, but I cannot edit a page that already exists. I get the following error – “that webpage does not exist”. This literally started happening overnight.

I’m running WP 4 and elegant themes “The Professional”. Just updated WP and the theme to the latest versions to no avail.

Thanks.