SL install disk keeps ejecting

I searched, but I must suck at it....

The Snow Leopard install disk spins up and seems to be starting up, then it ejects from the CD drive. I am clueless...

This is on an Intel MacBook Pro that's a couple years old currently running Leopard.

And no, it's not a restore disk from another machine. I was told it's the retail version, iLife/iWork/SnowL package.

Thanks in advance for your help.

Phil

 

anyone?