Entered Credentials are Incorrect

Hi Everyone:

I have a little mystery going on. I host several WordPress sites and every once in a while people can’t login to any of the sites. I noticed when trying to troubleshoot this issue is when I go to any of the login pages. When the wp-login page loads up, it automatically gives me the message “ERROR: Entered credentials are incorrect” . Has anyone experienced this issue before? Any help would be greatly appreciated. Im scratching my head on how to solve this one.