Question: There are so many different versions of the Softdevices, how do I chose the right Version of Softdevice + program-Application?
Please tell me which Version of SDK and Softdevice you are working with.

 
Answer: You need to make attention to the compatibility between the SDK and Soft Device versions you are using. You can find information on the Nordic infocenter website in section nRF51 series > nRF51 Series IC revisions compatibility with SDK and SoftDevice http://infocenter.nordicsemi.com/index.jsp