In such case, the chip may be secured or the code in flash might put it in a low power mode and not permit a debug connection. Since you only have the possibility to use the embedded Segger J-Link probe, you have to recover the part by opening the JLink.exe application which comes with the Segger package installation and type the, unlock kinetis command.
The latest Segger J-Link package can be found here:
http://www.segger.com/cms/jlink-software.html
There are several ways how a chip can get secured, including bugs in the silicon, or that you download the wrong image to the target, ending up writing/flashing the security areas of the chip. In such cases the P&E connections, the P&E firmware is able to handle unsecure directly, means you are not required to use an external utility as in the case for J-Link.