Some malicious code can change the permissions of a file.
If you are an admin then you can
Edit the permissions of the file so you will have full access again.
1. Right click on the file... Click Properties
2. Click the Security tab, then click the Advanced button.
3. In the permissions tab, Select either the administrator or your user account, then click Edit...
4. Everything under the Allow column should be checked.
5. Click ok.
Hope this helps.