I signed up with an email like username+label@gmail.com. This helps me better organize and it works with GMail. Problem is that even after confirming the email

I signed up with an email like username+label@gmail.com. This helps me better organize and it works with GMail. Problem is that even after confirming the email address, when attempting to login it errors out: Please enter a correct username and password. Note that both fields are case-sensitive. I've reset the password and still the same error. I wonder how much of it has to do with the email address format and if you are cleaning invalid characters, etc.