How to avoid login problem that was created in backend

Hi friends,

In magento some times customer login page displayed invalid user name or password error message display

Reason for that errors

1. Give correct user name and password that will check in back end customer-> manage customer-> change the password and then work
2. Another important process is
3. If we create customer login in back end it does-not work properly because

• Goto->system->configuration-> customer configuration-> click that
• Then click Account Sharing Information
• and change the Share Customer Accounts -> change into Global
• then check in front end
• it work nice.