Mavericks and Time Machine

Hi to all, I have a little question. I have downloaded from App Store the upgrade to Mavericks, when i try to execute and install the upgrade the installer shows to me a message : This disk is used from Time Machine back up, but i've used Time Machine only with external hard disks and not with the hard disk of my Mac Book Pro. Do you have any answers for my problem? I don't want to install Mavericks from zero. Can you help me?

Thank you all!!!