Check the properties for your C:// drive itself. Also, do any folders involved show an icon with a lock on it? Check the C drive itself, Program Files -> iTunes & down, Program Files (x86) -> iTunes & down, Program Data -> iTunes & down, and Users -> [name] & down. WARNING, DO NOT TAKE OWNERSHIP of the C: (Windows 7) drive!!
Have you simply been clicking "continue" in a window similar to this:
Or have you actually gone through the "Take Ownership" procedure? Here's a tutorial for installing a shortcut in the right-click menu: Take Ownership Shortcut
On the other hand, here's an instant remedy.
The simplest way to fix this, albeit wouldn't find the actual cause, would be to move to the other account. Make it an administrator. Move your data files. Then just delete the original account.