Your configuration folder may have become corrupted. You can rename the configuration folder to have Dreamweaver recreate it. Close Dreamweaver and go to:
C:\Users\<Your User Name>\AppData\Roaming\Macromedia\Dreamweaver 8
(Please note that <Your User Name> Should be replaced with the User name you use to log into your computer)
Rename the configuration folder to configuration_back. This will have the effect of disabling all of the installed extensions. You should open the extension manager and remove all extensions to clear the extension mangers cache. After removing the extensions you can then reinstall them making sure to download the latest versions from your order history.
On Windows Computers, The AppData or Application Data folders may be set to be hidden.
To View Hidden Folders in Windows Vista:
1) In The Windows Explorer, Click the "Organize" button
2) Select "Folders And Search Options"
3) Select the "View" tab
4) Click the "Show Hidden Folders And Files" radio button.