Users having to login again

[trundle]

I am having an issue, where my users log into the site, proceed to add items to their cart, then when they try and checkout, it prompts them to log in again. It doesn't happen all the time, but once in a while. The users are not going over the Control Panel Session Expiration, which is set to 120, they are on on for about 45 minutes. DO you know why this would happen or where I can check to see why it is happening?  Thank you

[Basara]

Hello.
The PHP session expiration is handled by your server.
You must check with your hosting provider what is the server session expiration time and is any issue with it.
Make sure that session path is writable