2 quick questions
1. Was fast provisioning NOT enabled on the Source Datastore?
2. Were you attempting to SvMotion the VM to a datastore that is also in the same Organization vDC in vCloud Director?
If both of the above statements are true, then it's just like any other SvMotion. If either is false, then it's an unsupported scenario.
Should both be true, then check out any troubleshooting related to SvMotion =)
Best Regards,
Jon Hemming