The Stand alone version of CSS Menu writer is not compatible with DW CS 6
The Extensions that we offer that are compatible with DW CS are:
eCart 5
Free Tools
Design Extender
Data Bridge.
the Design Extender extension includes all of our design centered extensions like CSS Menu writer.
You will need to upgrade to Design Extender in order to use Menu Writer in that version of Dreamweaver, other wise, you should revert to the older DW version you had been using when you purchased Menu Writer initialy.