We run the NarPackager command from an ant script without problems on Linux.

Among other things, the log shows:
     [echo] Running CmdLineNarPackager -conf /home/rsivan/pv/trunk/Packager.xml
     [echo] Classpath set to: /home/rsivan/pv/trunk/TOOLS/zoho/plugins/com.adventnet.nms.EMSDevelopment_1.1.0.jar
     [java] Make file list for dir:/home/rsivan/pv/trunk/classes
     [java] ProVisionMRV_Server.jar is not created since class file is not present in the classes folder
...

A similar operation on Windows tries to incorporate (and even modify) that jar:
     [echo] Running CmdLineNarPackager -conf c:/PV/pv/Packager.xml
     [echo] Classpath set to: c:/PV/pv/TOOLS/zoho/plugins/com.adventnet.nms.EMSDevelopment_1.1.0.jar
     [java] Make file list for dir:c:\PV\pv\classes
     [java] Jar file Name osc:\PV\pv\ProVisionMRV_Server.jar
...

I'll appreciate any help.
Thanks
  Reuben