It say they cannot find an active account with the user name and password
Is this after you have deleted cookies and temporary Internet files? If so, how did you make this post?
You do raise an interesting point. We do have some member, who never log out. If they delete cookies, the forum will show them as logged out and they can't get back in because they no longer remember their password. Thankfully, the login in screen has a "forgot password" link.
We did have a member that happened to and they no longer had the email account they registered with. Their only recourse was to create a new forum account.