Strangeness in getting ACLs for .pst files

I have the need to determine the ACLs for a range of files and have found code-snippets and such that have helped and for the most part seem to work well. However, one thing is beyond me at the moment:

1) Get-ACL: Get-Acl on a .pst file, it gives me an error, no matter the location of the file, whether it is open in outlook or not, no matter of size or such things. I can see the file with Get-ChildItem, and indeed using icacls at the command line or the Windows Explorer Properties menu, I can get the acl information. So acl info is there and exists. But when I try the get-acl command, I get the following:

PS C:\users\Shadow\Desktop> get-acl '.\PersonalFolders.pst'

get-acl : Attempted to perform an unauthorized operation.

At line:1 char:1

+ get-acl '.\PersonalFolders.pst'

+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

+ CategoryInfo : NotSpecified: (:) [Get-Acl], UnauthorizedAccessException

+ FullyQualifiedErrorId : System.UnauthorizedAccessException,Microsoft.PowerShell.Commands.GetAclCommand

As part of experimenting, I tried the get-acl command against a text file that had the pst extension, and it didn't work.   I renamed an actual pst file with another extension (such as .pdf) and it worked. 

I also tried the GetAccessControl command and it worked when applied to a non-pst file, such as:  (get-item 'f.pdf').getAccessControl().Access

Exception calling "GetAccessControl" with "0" argument(s): "Attempted to perform an unauthorized operation."

At line:1 char:2

+ (get-item '.\f.pst').getAccessControl().Access

+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException

+ FullyQualifiedErrorId : UnauthorizedAccessException

Suggestions? Thoughts?

Thanks in advance,

W