They're defenitely not DVD-Rs. I can't even open them in explorer, I just get that message. They're TDK audio cds. A couple of them were normal maxel cd-rs and they worked fine, so I thought it might be the audio disc thing. I guess if thats not the problem then I need to try one of the options wazoo2u suggested.

If anyone else knows anything that might cause this, your help is appreciated. Thanks!