Hi narendran201110141. I ran into this & discovered that it occurs when an existing vmdk having the same name as the svmotion source vmdk exists on the target datastore. It does not occur if there is no disk having the same name existing on the target datastore. I opened an SR on this & VMware support reproduced this behavior as well. They have created a new KB as a result: http://kb.vmware.com/kb/2053056. This existing KB is close but not exact match : http://kb.vmware.com/kb/2008877. This behavior is fixed in 5.1U1, but I am currently running 5.0 U2 & haven't tested this yet.
Kind regards,
~Russ