I am having this exact same issue. I know it's not username, password, or pin, because when one of those is wrong, I get the typical incorrect info message. I also know I am not locked out, since the last time I tried was over two and a half hours ago. Also, if I click on "Control Panel" after getting this message, I am not returned to the login screen. The message stays up, but now I have "Logout" as an option on the left side menu. I have to click it to get back to the login screen.
Message with correct info is:
"Oh. Something went wrong. :( Internal Server Error"
Message with incorrect pw:
"Invalid credentials"
Message with incorrect pin:
"The verification code is not valid"