a) Are you performing a complete PC backup?
b) Do you have complete file permission to the files you are backing up and to the destination you are saving the back up?
As a workaround you need to follow the steps provided below.
Check the permissions of the file or of the folder the file is saved in. Here's how:
1. Right-click the file or folder, and then click
Properties.
2. Click the
Security tab.
3.
Under Group or user names, click your name to see the permissions you have.
To open a file, you need to have read permission.
Check to see if the file is encrypted. Here's how:
4. Right-click the file, and then click
Properties.
5. Click the
General tab, and then click
Advanced.
If the Encrypt contents to secure data check box is selected, you need the certificate that was used to encrypt the file to open it.
If you find any difficulty in performing the above provided steps then you may follow the link below.
How do I open a file if I get an access denied message?
http://windows.microsoft.com/en-US/Windows7/How-do-I-open-a-file-if-I-get-an-access-denied-message 