Fedora 15: sda must have a gpt disk label

[Derek Tattersall]

I am trying to install F15 on a Lenovo X120E laptop.

When I get to the disk partitioning step, it tells me:

sda must have a GPT disk label

What is a GPT disk label, and how do I get one?

By the way, Ubuntu installed just fine. I am trying to delete the Ubuntu 
partition and install Fedora on it instead, without wiping out windows.

Thanks.

Derek Tattersall