thanks Stumpr

i am using vsphere web services sdk 4 that was released on 29th May 2009. i download it from this location

http://www.vmware.com/support/developer/vc-sdk/

i am extracting it and running build2005 script as mentioned in the documentation

i have looked in to my wsdl file i.e. vim25.wsdl and it does contain VirtualMachineRelocateDiskMoveOptions. But when i look in to the object browser of the reference to Vim25Service2005.dll, i dont see VirtualMachineRelocateDiskMoveOptions there.