I put the disk in my Mac and it tells me it is blank.

Solution For some odd reason the occasional Mac drive has a problem reading certain brands of media.
If you take the disk to another system (even a PC) you'll see that the disk is not blank.

If you encounter this oddity, then copy the disk contents onto another system's hard drive and burn a fresh DVD of the contents and try the new disk instead.
That should solve your issue.