Delete the Dreamweaver Preferences folder and relaunch Dreamweaver. For detailed instructions, see this article.
If the issue is still not resolved, report the problem to Adobe by using the Help > Submit Bug/Feature Request option. Ensure that you attach the log files to your report. You can find the log files at the following locations:
- Windows: C:\Users\<username>\AppData\Roaming\Adobe\Dreamweaver CC 2015\en_US\Configuration\Updates\Log
- Mac: ~/Library/Application Support/Adobe/Dreamweaver CC 2015/en_US/Configuration/Updates/Log