Your external drive is formatted with the NTFS file system, which supports access restrictions.
Unfortunately, while some users and security groups are built-in to Windows with predefined Security IDs which are the same on all machines (such as Everyone), other users and groups have SIDs derived from the machine they're defined on.
To normalize the situation you should:
- While logged-in as Administrator,
right-click the drive's root
directory and select Properties.
- Click the Security tab, then the
- In the Advanced Security Settings
dialog for the drive, click the
Owner tab, then the Edit button.
- Click the Administrators group,
check Replace owner on
subcontainers and objects and
click OK. If asked about replacing
existing permissions with ones
giving you Full Control, click Yes.
- Back in the Security tab and on the
original Properties sheet again,
click the Edit button, and in the
Security dialog click Remove for all
entries for all accounts listed under "Group or user names",
except for the well-known ones of
System, Administrators, Users and
- Click Add, and in the "Select Users,
Computer or Groups" dialog under
"Enter the object names to select",
Everyone and click OK. You
should verify that
Everyone has been
added to the list.
- Click Everyone, check Full Control,
then click on Apply.
- Click Advanced again to go back to
the Advanced Security Settings
dialog box and click the Change Permissions button. Check Replace
permission entries on all child
objects and click OK and OK.
- Click OK.
Be careful in the future not to allocate separate access permissions to sub-folders of the drive (leaving all permissions as inherited). If this happens again, repeat the step for "Replace permission entries on all child objects".
Be mindful of the fact that under Windows 7/8 the Guest account is not part of the Everyone group. If you need it, you'll have to add Guest as above for the Everyone group.
If you encounter problems with UAC, try using Explorer via "Run as administrator".