It sounds as though Windows 7 may be recognizing the drive as a foreign hard disk drive. Both of you may benefit from the following TechNet forum thread Access denied to external Hard Drive on Windows 7
where a member of the Microsoft Contingent Staff, Wpbacon, provides the necessary steps to resolve a foreign disk issue.
For additional assistance regarding Windows 7 and how it accesses connected hard disks you may find the following resource article Troubleshooting Disk Management
Windows Outreach Team – IT Pro