Sorry for the delay.
I've tried your suggestion to update the system and reinstallation of the Guest Additions, but unfortunately the problem persists.
Even a complete reinstall of the virtual machine didn't do much.
I've been searching the web a lot last week searching for a solution and it appears that more people experience a similar issue, but the solutions they provide does not work for me.
I'm completely out of ideas, is there perhaps anything left I could try to do?
Last edited by Thomas.; 04-22-2013 at 02:06 PM.