I have a Joomla 1.5 website that has a problem - when you login, it doesn't log you in and says "Your session has expired. Please log in again." as a blue error message. However the page it is on is titled "Registered Area" and then says "Welcome to the registered user area of our site.".
I go through the cart and the details are not logged in so you have to login again, and it works.
Why is this? I haven't done anything to the site recently.