Login error & wont stay logged in

Hi, I have been using UM for a while with no issues. Just recently, I noticed that I get this error when logging in: “An error has been encountered. Probably page was cached. Please try again.” I just hit login again & it worked, but when I move to another page in the site, I don’t stay logged in. This is bad for me because my users must be logged in to access the content. If someone can help me out with this I’d greatly appreciate it.

The page I need help with: [log in to see the link]