CSS Menu writer is not compatible with DW CS6 at this time, you will need to use it in a previous version of Dreamweaver, or you could upgrade to data Bridge which includes CSS menu writer and other extensions in a CS6 compatible package.
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.