NFS Underground GC Issue

Hope someone can help enlighten me here on this one.

I just bought a copy of NFS Underground at the local store for my daughter. I have her gamecube modded with a Qoob Pro chip. I backed it up and made a copy of it but it won't play. Says it is NO ISO9660 DVD found!

Anyone know by chance what this error could mean? The other games I purchased and backed up work fine but not this one. Something I am doing wrong? Or should it be ripped specifically and with a specific program?

The ISO file size ripped is: 1,459,978,240. Just like the other games I made backups of and are working.

And also both the working game backup of the other game and the backup of the NFS Underground were burnt onto the same media.

Thanks for any help.

Flandrel