If you should see this error message when you launch Dragon NaturallySpeaking:
"The file C:\WINDOWS\speech\speech.dll is version 4.0.x.xxxx. NaturallySpeaking requires version 126.96.36.1992 to run reliably."
you probably need to reinstall the Microsoft Speech API.
An application programming interface (API) allows one software program to interact with another software program.
If the Microsoft Speech API is not recognized properly by Dragon NaturallySpeaking then Dragon cannot launch properly and you may see the above error message.
Refer to this link at the Nuance Support Knowledge Base for additional information and also to download a file that will reinstall the Microsoft Speech API: