EFS Share issue

I have vista ultimate on a notebook and desktop. I use synctoy to sync
documents from desktop to a usb drive and also from notebook to same usb
drive. The usb is my holding vessel for shared files. I activated efs and
exported the key so it resides on both the notebook and desktop. Why then am
i getting an error in both sync toy and windows explorer resulting in the
inability to copy the file. I even tried copying it manually to test the
cross hardware compatibility to copy and open the encrypted files. It seems
to me if the key is on both machines and the username/passwords are the same
as well as the directory structures and user rights i should be able to sync
these encrypted files.