This is a bug that I have reported to Adobe. It doesn't happen all the time, but it happens on occasion when uninstalling extensions that have a floating panel.
To fix this issue, go to the upper right corner of the application to the "workspace" drop menu, which should be to the left of the search field. If you click the down arrow, and select Reset "Designer" (or whatever workspace you're working with. Then restart Dreamweaver to see if that has corrected the issue.
If that hasn't fixed the issue, please post back.