The long row of numbers that you see in the list of accounts on the security tab is called a SID (or Security ID). When Windows can't recognize the security identifier associated to the file ACLs (Access Control List / Permissions) it displays the SID. Normally Windows will be able to translate that SID in to an account name or alias, such as 'DOMAIN\Username'.
It looks like the original permissions are still associated to the files you're trying to access and they're considered foreign to the computer you're trying to access them from. In order to open these files you will need to take ownership of them and give yourself access to read (and/or write/modify/delete). This is where the error message comes in. "The requested operation requires elevation" means that in order to open the file you'll need the elevated permission of a local administrator to take ownership and gain access.
You may already be logged on your system as a user that is a member of the local administrators, however Vista, Windows 7, and Windows Server 2008 offer additional layers of Security to help protect your system. This is called UAC or User Access Control. Basically even though you're on as administrator Windows protects certain administrative functions with another security layer. You've probably seen the screen get dimmed and a dialogue asking you if you want to Continue or Cancel a certain operation. This is UAC asking if you're really really really sure you want to do what you're about to do and making sure you're the one trying to do it and not a rouge process or virus trying to take over.
In order to change the ownership of the files you can...
1. go in to the properties of the folder that contains the files you need to take ownership of
2. click on the security tab
3. click Advanced
4. click on the Owner tab
5. Click Edit...
6. Select the account name in the Change owner to list that you want to take ownership
7. Check the box, Replace owner on subcontainers and objects
8. Click OK
The ownership information will be updated on all of the objects in the folder including subcontainers (or the subfolders). Depending on how many files and folders there are under your starting point this make take some time to complete. Once it's down you will be able to modify the Security permissions as you wish for the files and folders (such as Full Control, Read Only, Read & Write, etc).
NOTE: If you're not logged on as an administrator on your system, the above steps will not work as taking over file object ownership requires administrator privledges.