[TYPO3-english] [felogin] login failure despite right user data

[Robert Jędruszek]

I'm trying to implement a login and password. When I fill a form with 
correct data login (the same as in fe_users table), the login fails - 
message:

"Login failure
An error occurred during login. Most likely you didn't enter the 
username or password correctly. Be certain that you enter them precisely 
as they are, including upper/lower case. Another possibility is that 
cookies might be disabled in your webbrowser."

What could be the cause of this behavior?