fatal error call to a member function getusername() on a non-object in magento

Hello Friend,

when you get like this error "

Fatal error: Call to a member function getUsername() on a non-object in .../app/design/adminhtml/default/default/template/page/header.phtml on line 31".

Please  follow the steps

1. Backup the var folder as (var-back)
2. Create a new var directory
3. Backup the locks folder as (locks-back) {if available}
4. Create the locks directory

Thanks
Enjoy Your Self,