please provide some more details:
What is your OS?
What version of Dreamweaver?
What extensions including the version numbers are installed?
What are the exact steps you are taking to producer the error?
have you tried 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:
http://www.webassist.com/tutorials/Common-installation-issues