If you get failed to launch UI automation server error massage with your latest dragon version 15.6, then there are few steps you need to follow
Step one: First check your UAC settings, it should be like this,
If your UAC looks like this, then follow next step or change your UAC to this mode and restart the computer, it will solve the issue.
If no: Please change your UAC setting to Notify me only when apps try to make changes to my computer (default)
Step Two: If issue is still persisting then please uninstall the Dragon program and reinstall it.
If you want to know how to uninstall and reinstall the Dragon program please check the below link.