what extensions, including the version number are installed?
only the recent Design Extender, Data Bridge, eCart 5 and Free Tools extension are compatible with DW CS6, if you have the previous stand alone extension versions, you will either need to upgrade to the newer ones, or continue using the previous DW version.
if you are using the current versions, make sure to install in this order:
eCart 5
Free Tools
Design Extender
Data Bridge