On Unix systems, when a process fails the kernel will produce a "core" file so that developers can use it for debugging.
Try executing "file /usr/nr/var/new/core" to find out for which process the core file was created.
I would remove the core file, and stop and start the netranger processes.
Then keep an eye on the system for the next few days.
If no new core files appear then it was possibly a one time ocurrence.
If new core files appear then check the process that created it.
If it is an operating system command, then you would need to check with the operating system vendor. (On a director you would have to check with Sun or HP, if this was on the sensor itself then you would contact the TAC since Cisco supports the OS on the sensor appliance).
If it is a netranger process that is causing the core file, then check through previous DDTS Issues, if you can't find an open issue then contact the TAC.