try this it worked for me. this problem was making my head want to burst. when you do these instructions at the link below, don't forget to go to the itunes preference and then advance tabs and change the folder location...this is the advice i got from a response to my post...
This is your root problem. Use Windows Device Manager to
*permanently* assign the drive letter for both exHD.
http://support.microsoft.com/kb/307844