Permissions to access cloned hard drive files and folders denied

Hi, I have a cloned hard drive of my home PC in a caddy which I'm trying to access (USB) from my work PC. But it's telling me I don't have permission to access files or folders.

Edit- sorted individual folders but not contained files so it would be useful to know how to apply changes to the file tree. I had to find different user options, 'Administrator', 'Everyone' etc, from right click-properties-security-advanced-change-advanced-'find now' option rather than trying to type them in.

Anyone know how to apply this change to the file tree under a drive letter, or even under 'documents' would be useful. Also I assume I would have to change permissions again if I ever needed to put this clone back into my home PC? (I created it as a quick change backup, but perhaps also trying to use it like a large memory stick to take files to work isn't going to be worth the bother.) Thanks.

I found the earlier post by Tully -'Can't delete folder', with a similar permissions problem, and followed the steps in the reply by CountMike which included 'select a principal'. This appeared to work until it repeatedly came up with the error message, 'failed to enumerate objects in container' regarding different files.

Edit: going back to my previous route as in my first post I found the 'replace owner on subcontainer and objects' box which only appears after you've done one of the 'OK' stages; useful. This gave me access to folders but not indivisual files, I had to go through the process again for a file.