While on Windows 8 Pro, I created 2 users both in the Administrator Group but changed permissions on one user's folders for privacy. Somehow things got mixed up and I couldn't install some applications from this user (maybe all applications but I'm not sure). For example I was trying to install the software "AirParrot" and always got the error message was:

Error reading from C:\Users\user2\Downloads\AirParrot32.msi. Verify that the file exists and that you can access it. 

As you can see this is an MSI (Microsoft Installer) file and I always got this error message on MSI files (not sure about the .exe ones). I tried searching all over the internet but for solutions on how to mass reset permissions to the user's folders but no solution seemed solid. Well what I finally found is that "System" user must be able to access the file that you need to install. And guess what ... my folders where missing the "System" user completely. So here's what I did:

1. Right click the User's folder (user2 in my case) and select Properties
2. Select the "Security" tab
3. Click "Edit"
4. Click "Add"
5. Type "System" (without quotes), then search and if the name is shown correctly click "OK"
6. From what I understood, the System user must have Read&Execute permissions so at least check these and select OK (Windows will automatically select List, Read and Write permissions to satisfy the Read & Execute demand)
7. Finally, select "Apply" on the last dialog and wait for the Permissions to apply to all subfolders. This might and WILL take some time depending on the number of folders and files on your User Directory.

If the installations still give you trouble you might have to give Full Control in the permissions tab. But I have my worries on whether this poses a security threat? Dunno. Try it out.