Norton Ghost 10.0 - Disk Full

Hello,

 

My parents have a Dell computer with what I believe was called the 'Datasafe' option.  It has a pair of identical hard disks and included Ghost 10.0 to backup the one disk to the other

 

Recently they've been getting this message:

Description: Error EC8F17B7: Cannot create recovery points for job: Complete system backup.

Error EA390719: Target disk full.  Error EA390719: Target disk full.

Details: 0xEBAB0005

It sounds like the back up disk is full.  I live a couple hundred miles away and don't know what to tell them to do to fix it.  They aren't very computer savy.  I think if I was sitting at the PC, I could figure it out, but I am not.

 

How can they correct this problem?

 

Thanks.