if you get "access denied" errors when trying to save the file, try openning the file using "Run as Administrator". this issue happens usually when you're working on Win Vista/7 with UAC turned on.
on Win8 you can't just edit the file and save it on it's original location. instead, edit the file and save it on the Desktop. later replace the original file with the new one you saved on the desktop using the file explorer's Copy-Paste. You will probably be asked to confirm the action using Administrator account.