I think I have solved it. Here's what I did
- Enable system administrator account from command promt.
- Log in as the system administrator
- Select the Windows folder in the installation root
- Open its security properties, click 'Advanced', go to 'Owner' tab and click 'Edit'
- Select 'Administrator' (not 'Administrators'). Check 'Replace owners on subcontainers and objects' option
- Click 'Ok'. It'll confirm the action and take 2-3 minutes to set permissions on folder and sub-folders
- Now close the properties dialogue box and open it again (required after changing ownership)
- Again go to the security tab, click 'Edit' to edit permissions. Select 'Administrators' (either one)
- In the pane below, check the box under the 'Allow' column, and on the 'Full control' row
- Verify that all check boxes are checked (this grants full permission to the Administrator account to do whatever the user desires with the files and folders inside the Windows directory)
- If this doesn't work, as suggested above by John, while changing ownership, verify that "Include inheritable permissions from this object's parent" option is unchecked
Of course this creates a security risk, but I am willing to accept the risk at the benefit of no interruption while changing system files. God Windows is stupid.
Thanks for your help and prompt replies, John.