Moving VM between vCenters

Hi Guys,

I am in process of moving VMs from Vcenter 5.1 to vCenter 5.5.

Esxi hosts in VC 5.1 and VC5.5 have access to same datastore.

In order to move

1. Switch off vm on vc5.2.
2. Removed VM from Inventory.
3. On VC 5.5 opened VMs .vmx file to registed the VM to VC5.5.
4. I got pop-up message saying "This virtual machine might have been moved or copied. In order to configure certain management and networking features,

VMware ESX needs to know if this virtual machine was moved or copied. If you don't know, answer "button.uuid.copiedTheVM".

I choose option that I moved it. Why should I get this message? What happens if choose I moved it ?and what happens if I choose I copied it ?

Thanks...