Site Import 2 is not compatible with Dreamweaver CS6. I believe the latest version of Dreamweaver that site Import 2 would be compatible with would be CS4.
It was replaced By Site Import 3, then by Site Import in Design Extender.
You would need to upgrade to design Extender in order to use Site Import in DW CS6, or continue using V2 in the previous version of Dreamweaver.