CS6 - License is being marked as invalid during install

I am migrating a customer from one PC to a new PC and they would like the install of CS6 moved.  We uninstalled and deactivated the install and then downloaded CS6 and tried to input the serial number, and I was presented with the error message that the serial number was invalid.  Adobe Chat Support has been unable to assist me with this issue in determining why the license was marked as invalid and if there are any steps to revalidate it as my customer is insistent that they have been working with is a genuine Adobe product.