Azure service bus AddMessage returns 401

The following AddMessage call (code borrowed from another post) fails with "The remote server retued an error: (401) Unauthorized."

var queue = new CloudQueueClient(
     new Uri("https://<service-account>.servicebus.windows.net/"), 
     new StorageCredentials("access1", "xxx")).GetQueueReference("queue1");

queue.AddMessage(new CloudQueueMessage("Hello"));

Where xxx is the 44-character PRIMARY KEY copied from Azure's configuration screen. It doesn't contain any 'special' characters. Can anyone see where I'm going wrong? Using the service level Service Access Policy credentials gives the same 401 error.

This is the Azure policy configuration for my service-account.

(I did try another approach, but hit another snag service bus coection-string problem)