command line - cmd > attrib - Unable to change attribute

I'm following this tutorial because I'm having problems with the Task Scheduler service:
http://technicallyeasy.net/2010/10/how-to-fix-keyset-does-not-exist-for-scheduled-tasks-in-windows/

Basically (in case the link dies), it says that you should go to C:\Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\S-1-5-18 and delete everything that's in there.

Here's the problem I'm having - there is a single file, marked as hidden, system and read-only. The file name is "d42cc0c3858a58db2db37658219e6400_46884bcb-8fba-461e-a2ee-e996218ba78a".
When I try to delete it, I get the following message:
Cannot delete X : Make sure you specifiy the correct path

The file is definitely there, as I can browse to it via Windows Explorer.
I assumed that the problem is the "system" attribute.
I ran
attrib -s "path\to\the\file"

and the output:
Unable to change attribute - "path\to\the\file"

When I try to remove the hidden or read-only attributes instead, I get:
Not resetting system file - "path\to\the\file"

Once again, this is a file, not a folder.
Any ideas greatly appreciated!

PS: OS is Windows Server 2003 r2 x64