Page password protection problem

I have one page on my website that was password protected and was working fine for several months. Recently, I checked and found that the page was inaccessible via the password. As admin, I verified that the password was the one I had set. Could not access the page, so I deleted the password and verified that the page was then accessible. But no matter what password I now set, I cannot access the page except by going in as admin and deleting the password. Any hints?