What extensions including the version numbers are installed?
The Free Tools system requirements are a Minimum of DW CS4, so it will not be compatible with DW CS3.
try reseting the workspace layout:
go to Window -> Work Space layout -> Reset '<your layout name>'
and Delete the Dreamweaver Cache file from the users configuration folder:
also try disabling the preview, go to webassist -> Preferences.
in the preview section select the disable preview option.