Maintain Session

Hey, I am stumped. Am hoping for some research ideas.
Here's the deal.

I have a 2-PC home network. One PC runs XP Pro; the other XP Home. Otherwise they are the same. Browsers configured the same also.
They share an Internet connection via router to a DSL modem.

I just uploaded a php application to a new web host.

On the XP pro machione I can login and maintain session from page to page.

But on the XP Home machine, I log in successfully. Then when calling any other page, I lose session (and access) so I am kicked out of the application.

Same application.
Same browser configuration.

Any ideas?