[londoner]

yeah, have you protected a folder in your cpanel? Go to your cpanel > password protected directories, and see which directories u have protected.
Any directory protected will have a lock icon next to it, you might've protected the wrong folder by mistake, so what you do is click that folder and uncheck "password protect directory".

If you were trying to protect your admincp then Only protect that directory and nothing else.
cpanel > password protect directories > choose web root.

click admincp folder (whatever you have it called), and check password protect directory, and add a user if you haven't already.

Other than that can you please specify which folder you tried to protect if any.
Thanks.