Cluster.Create Manager throws HTTP401 UnAuthorized ERROR

I am trying to connect to couchbase cluster to create a new Bucket using ClusterManager.

COuchbase Server: Version: 3.0.2-1603 Enterprise Edition (build-1603)
Below is the code snippet in .NET SDK 2.0.

var couchbaseInstances = new List<Uri>()

;
var config = new ClientConfiguration()
{
ViewRequestTimeout = 45000,
Servers = couchbaseInstances,
PoolConfiguration = new PoolConfiguration

};
var cluster = new Cluster(config);
var clusterManager = cluster.CreateManager(userName, password);
var result = clusterManager.CreateBucket(bucketName);

But I get 401 UnAuthorized exception. I used the same userid and password that I use to login to the Couchbase web console.

Below is the forum link where I posted this question when I faced it for the first time.
https://forums.couchbase.com/t/connecting-to-couchbase-cluster-401-unauthorized/3607