When you look at the file's properties Security dialog
is anything checked for any group in the Deny column ?
You must highlight each group listed one at a time and
then look at what is Granted/Denied.
An account that is only in Administrators group is
actually also in other things to which there can be
NTFS Grants/Denies, like Authenticated Users,
Network, Interactive, Everyone. . . .
Not having EFS authorization appears as if it is a
NTFS permissions denial.  You should use the cipher
commandline utility to examine the thumbprint info of
the file to see what accounts are allowed to decrypt it.

This sounds like a file ownership issue related to NTFS.  Note, file
ownership and permissions supersede administrator rights.  How you resolve
it depends upon which version of XP you are running.

XP-Home

Unfortunately, XP Home using NTFS is essentially hard wired for "Simple File
Sharing" at system level.

However, you can set XP Home permissions in Safe Mode.  Reboot, and start
hitting F8, a menu should eventually appear and one of the
options is Safe Mode.  Select it.  Note, it will ask for the administrator's
password.  This is not your administrator account, rather it is the
machine's administrator account for which users are asked to create a
password during setup.

If you created no such password, when requested, leave blank and press
enter.

Open Explorer, go to Tools and Folder Options, on the view tab, scroll to
the bottom of the list, if it shows "Enable Simple File Sharing" deselect it
and click apply and ok.  If it shows nothing or won't let you make a change,
move on to the next step.

Navigate to the files, right click, select properties, go to the Security
tab, click advanced, go to the Owner tab and select the user that was logged
on when you were refused permission to access the files.  Click apply and
ok.  Close the properties box, reopen it, click add and type in the name of
the user you just enabled.  If you wish to set ownership for everything in
the folder, at the bottom of the Owner tab is the following selection:
"Replace owner on subcontainers and objects," select it as well.

Once complete, you should be able to do what you wish with these files when
you log back on as that user.

XP-Pro

If you have XP Pro, temporarily change the limited account to
administrative.  First, go to Windows Explorer, go to Tools, select Folder
Options, go to the View tab and be sure "Use Simple File Sharing" is not
selected.  If it is, deselect it and click apply and ok.

If you wish everything in a specific folder to be accessible to a user,
right click the folder, select properties, go to the Security tab, click
Advanced, go to the Owner tab,
select the user you wish to have access, at the bottom of the box, you
should see a check box for "Replace owner on subcontainers and objects,"
place a check in the box and click apply and ok.

The user should now be able to perform necessary functions on files in the
folder even as a limited account.  If not, make it an admin account again,
right click the folder, select Properties, go to the Security tab and be
sure the user is listed in the user list.  If not, click add and type the
user name in the appropriate box, be sure the user has all the necessary
permissions checked in the permission list below the user list, click apply
and ok.

That should do it and allow whatever access you desire for that folder even
in a limited account.

--
Michael Solomon MS-MVP
Windows Shell/User
Backup is a PC User's Best Friend
DTS-L.Org: http://www.dts-l.org/

I believe that we earlier resolved that it is not an
NTFS permissions issue.
Administrator is a recovery agent only in Windows 2000.
Windows XP has no recovery agent until one is configured
or the machine is joined to an Active Directory.