See http://support.microsoft.com/?kbid=308421 "How to take
ownership of a file or folder in Windows XP".

Wormster wrote:

Somehow several documents have suddenly become inaccessable with the message:
"Unable to open document: user does not have access privileges." No
restrictions were set. The files were fine one day and the next couldn't be
opened. Can anyone suggest a solution please? Thank you.