Currently, adding a shard without the admin db selected produces a cryptic error:

mongos> db.runCommand(

{ 'addshard': "shard-1/localhost:30000,localhost:30001,localhost:30002" }

)
Wed Oct 5 11:22:46 uncaught exception: error

{ "$err" : "can't find a shard to put new db on", "code" : 10185 }

A google search reveals that a number of people have asked questions about this error. A message advising the use of "admin" ought to be implemented.