1. On the Start menu, click Run.
2. Type explorer.exe, and then press ENTER.
3. In My Computer, double-click the drive letter that corresponds to your external hard disk.
4. Right-click the Windows Live OneCare folder, and then click Properties.
5. On the Security tab, under Groups or user names, click either Administrators or your user name.
6. Next to Full Control, select the Allow check box, and then click Apply.
7. In the Windows Live OneCare folder, select the backup set folder, and then press DELETE.
All this information was found here
2. Type explorer.exe, and then press ENTER.
3. In My Computer, double-click the drive letter that corresponds to your external hard disk.
4. Right-click the Windows Live OneCare folder, and then click Properties.
5. On the Security tab, under Groups or user names, click either Administrators or your user name.
6. Next to Full Control, select the Allow check box, and then click Apply.
7. In the Windows Live OneCare folder, select the backup set folder, and then press DELETE.
All this information was found here