Shredder is only an extension of tools already built in to Windows. Use Windows to delete them - can't you view them in Windows Explorer?
If so hightlight and click Shift-Delete together and they are permanently deleted.
If it can't shred something it's just possible that perhaps those files were read -only or otherwise protected perhaps.
Technical Support might be able to help you better there. It's a free phone call or online chat and linked under Useful Links at the top of the page.