NoSQL Mongo extension causing java.lang.NullPointerException

Hi,
I have RM 2.4 server problem. I copied NoSQL (rmx_nosql-6.4.0) and text mining (rmx_text-6.4.1) extensions from RM Studio into server plugins directory. They load fine, I configured Mongo connection and it tests OK in config window. The server is trial version, running with Java jre-7u79 64bit on Windows7.

When I run a process with Mongo read it fails like this:

May 30, 2015 8:53:16 PM <unknown> <unknown>
INFO: Process context is: Macros: [_ra_user : admin, _ra_jobID : 28]; Input: []; Output: []
May 30, 2015 8:53:16 PM <unknown> <unknown>
INFO: No filename given for result file, using stdout for logging results!
May 30, 2015 8:53:16 PM <unknown> <unknown>
INFO: Process //_LOCAL/home/admin/test2mongo starts
May 30, 2015 8:53:16 PM <unknown> <unknown>
SEVERE: Process failed: java.lang.NullPointerException
May 30, 2015 8:53:16 PM <unknown> <unknown>
SEVERE: Here:           Process[1] (Process)
           subprocess 'Main Process'
       ==>   +- Read MongoDB[1] (Read MongoDB)
             +- JSON To Data[0] (JSON To Data)

Same process executes OK on RM Studio.
Anyone have any ideas about this issue?
Ozzy