After years of use, suddenly could no longer log in to ING Bank (in NL).
After searching, learned the only thing to do was either use another browser (!) or downgrade.
Downgrading was not difficult, from v. 12.(+) to 11.64. I can now log in again to ING Bank.
I have friends who have contacted me with the same problem, so I wanted to post it here if it may help anyone else.
Details: I did edit the index.ini file in the mailbox folder as suggested (in the Forum Topic, link below) and it worked the first time, including my mail and all preferences. (also History, Bookmarks, etc.)
Forum Topic: "How to downgrade to Opera 11.64 without mail problem"