This just happened today.
And it’s driving me crazy not being able to do anything since I had this error.
The website I am currently working on is set in two languages.
I have set the default store view in 2nd language and therefore admin login panel also gets diaplayed in 2nd language.
From the moment I set my default store in 2nd language, I get this login error all over the screen (see attached image).
Please help me out on this issue.
Many thanks.
Click thumbnail to see full-size image