Release : 10.0
Component : API GATEWAY
It is a java error; this is not a gateway specific error. And that the o/s is not allowing it to access the file.
The actual problem was related to the group permissions of the GMU folder.
>> chmod -R g+rwx <gmu folder>
The details of java error can be found in the following link.
https://docs.oracle.com/javase/8/docs/api/java/nio/file/AccessDeniedException.html