what other extensions do you have installed? There may be a conflict occurring due to another extension installed.
The quickest way to fix this sort of error is to rename the configuration folder.
Go to C:\users\John Hansen\Appdata\Roamaing\Dreamweaver CS5\en_us and rename the configuration folder to configuration_back
now open the extension manager, select each extension and click remove.
This should get Dreamweaver working again.
You can then