We have 3 node replicaset hosted on linux machines. Recently we added authentication restarted the replicaset. The following documentation was used:
http://docs.mongodb.org/manual/tutorial/deploy-replica-set-with-auth/

We use the following URI for connecting to Mongo:
mongodb://x1.mongodb.com,x2.mongodb.com,x3.mongodb.com/?replicaSet=r0

We changed that to the following:
mongodb://username:password@x1.mongodb.com,x2.mongodb.com,x3.mongodb.com/db?replicaSet=r0

After this c driver components no longer able to retrieve data from Mongo, although c# components are working fine.

We can also login to the replicaset from mongo console and query data.

Following are errors from Log:
1. assertion 13 not authorized for query on xxx.bbb ns:xxx.bbb query:{ $query:

}

2. Unauthorized not authorized on db to execute command