Hello. Sorry for commenting on such an old thread but I have the same error on prestashop 1.6.0.8. I can't login to BO for 1 week already. I have written about this problem at forge.prestashop.com but no answers. I have cleared cookies, cache, smarty, did all of the solutions written on the forums but none of them worked. Please help. Prestashop is starting to get very annoying with these strange errors coming out from nowhere...