Suddenly I'm requested to restore my iPhone to factory settings
Firstly I would sign up to iCloud if you haven't and then use the over the air backup to backup your iPhone (You get 5GB free!) then once this is done, you will be able to reset the phone should you want / need to.

Have there been any updates to your Virtual Box since your last sync? If not, it could be that iTunes can not see its XML file needed for device synchronisation; also ensure that all of the helper services are started on your machine.

Failing the above and assuming you follow the first recommendation, try resetting and restoring from iCloud. 

Best of luck