Alu iMac won't read DVD I just burned on it!

[Turboladdade]

I just burned an .dmg file to a double layer DVD using Disk Utility. The very computer I just burned it on won't read it, and says "you have inserted a blank DVD"

However, an iBook G4 I happen to have handy reads it just fine. What the???

The only thing I can think of that is even worth mentioning is that the disk image is only like 1 GB, while it has been burnt on a double layer DVD.

Any ideas would be greatly appreciated.