Session problem when trying to login through VirtualBox

[eluser]Unknown[/eluser]
I have a strange problem when I try to login through my Virtual Box. Somewhere between sessions being set and redirecting to my index page, the session userdata variable gets destroyed.

* When I type in my username and password and click login the userdata gets set as it's supposed to.
* Then I redirect to my index page.
* On the index page I do a check to see if the userdata is set. If it is the user can see the page, otherwise he gets redirected to the login page.
* I get redirected to the login page. If I print_r($this->sesion->userdata) at this stage. The only things that are set are: session_id, ip_adress, user_agent and last_activity. No userdata.

This problem is Only on VirtualBox and both on Chrome and IE.
Otherwise it works great on both Windows and Mac, with all browsers.

Is this a bug or anyone have any idea how I can fix it?

Edit:
Oh and also: SOMETIMES, logging in through VirtualBox works fine. Like every other day or so.