Hi Siva,
Yeah man great stuff thanks for the screen shot and the console output - this is why working with you is fun :-)))
So to me it seems to be a known issue of the VDDK 5.1 stated in its release notes there it reads:
- Disk Open fails without an SSL thumbprint from vCenter.
Whenever vCenter Server does not provide an SSL thumbprint for the target host, the VDDK library might core dump in the function VixDiskLib_Open(). This could happen (but does not always happen, depending on memory content) when vCenter Server 5.1 manages virtual disk on ESXi 5.0 and older hosts. A fix has been identified, and will be available in the VDDK 5.1 first update release.
If we now look at your provided console out put the last line reads:
Log: VixDiskLib: Thumprint for (null) not found in memory database
I would interpret this line as a hint to the known issue cited above.
Now you say you are quite sure the code worked at development time 2 months ago. Check if you used VDDK 5.0 or one of its update releases.
In other words try to run the code again using VDDK 5.0 Update 2.
Hope this is it ;-)