I'm having the same issue, and earlier today I got an error page no matter what I clicked on. I've been using this site for a LONG time, never had a problem before. Try signing in and out?
My 'Multi pages' works fine but 'Add photo' is malfunctioning
try private window or icognito
Update: I got the multi-page option to work after I cleared my browser's cache, cookies and history. Then I signed out of my mangago account, opened a fresh window and signed back in. Hope it works for you.
When I press "multi pages" it doesn't work, can anyone help?