Site Import 3 is not copmpatible with DW CS6, you would need to continue using it in your previous dreamweaver version or upgrade to Design Extener which has been upgraded to be compatible with DW CS6.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.