Do you see any errors in vSphere Client / Web Client when you attempt the migration?
Is the VM powered-on while you try to migrate it?
If it's on, then I assume that the tool you're using for migration attempts to create a snapshot. In case you created the virtual disk of 2TB simply by specifying 2 and TB as disk size, then it might be the snap issue described here: http://kb.vmware.com/kb/1012384
Does the migration fail when you try to re-locate VM in powered off state?
Can you try using Storage vMotion? If I'm right on above and it's the snap causing issues, then storage vMotion could help as since vSphere 5.0 it uses mirror driver to sync contents on source and destination datastores during live migration and does not create a snapshot.