Hi Vimal,
Try running the CCR directly without the Variant Saved.
OR
Try deleting/Editing the variant and save it again and then execute CCR from variant.
I guess some data (Tax related data) have been changed between the time the Variant got saved and your CCR execution.
Question - what you mean by " So before transferring the products, class & characteristics are transferred by then transferring the products."
Just my thoughts
Vinoth