Hi Mayuresh,
Thanks for the detailed query. 
I have the following customization :
QD activated,
for VCF : 00 Gas thermal factor, Fixed VCF.
Daily Calorific Values maintained.
With this I am able to execute estimation successfully. 
Can you check the error message description. Also you might have to tinker with the VCF procedure.
Cheers,
Rakesh..
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