Problem:
1.6.0 tools seems to validate camel case argument names, for example

vero:scripts$ ../../software/mongodb-osx-x86_64-1.6.0/bin/mongod --port 27000 --rest --shardsvr --replset replset0/ --dbpath /var/lib/mongodb/replset0 --fork --logpath /var/lib/mongodb/logs/server.log
ERROR: unknown option replset

The argument that is expected is "replSet". For O/S that are case sensitive (e.g. Mac, Linux, BSD etc.) this is a pain.

Workaround:
Modify the command line args that you are passing in

Solution:
I would suggest that
a) Argument names are unique, irrespective of case
b) The argument parser allows for camel and non-camel case versions