mongoDB Setup
Replica Set with all secondaries, no primary is up.

Sample Code:

var server = MongoServer.Create(ConfigurationManager.AppSettings["connectionString"]);
var db = server.GetDatabase("myDb", SafeMode.False);

var settings = db.CreateCollectionSettings<Task>("Tasks");
settings.SlaveOk = true;
settings.SafeMode = SafeMode.False;

var taskCollection = db.GetCollection(settings);

var tasks = taskCollection.FindAll();

var taskCount = taskCollection.Count();

I can get the collection of items fine from taskCollection.FindAll(), but if I call taskCollection.Count(), driver throws the following error:

MongoDB.Driver.MongoConnectionException: Unable to connect to the primary member of the replica set: No connection could be made because the target machine actively refused it

Some troubleshooting leads me to believe the MongoCollection.Count() implementation is not respecting the SlaveOk setting.