Hi,
May I ask what is that you are trying to do?
The disk name RHEL6x64bit-000009.vmdk - means there might be 9 snapshots present in the system already. You are referring the file from which snapshot? I am really not sure you should be using the function VixDiskLib_CreateChild on an Esx Host.
For QueryDiskChangedArea - you should post the exception that vSphereAPI throws for the call - that would really throw some light on the problem. But with this many snapshots I am thing you should be have done stun-unstun cycle - which might clear the problem.
Stun-unstun cycle:
1. Enable/disable ctkenabled
2. stop and start VM, or create and delete a snapshot.
./Siva.