C＃.NET MongoDriver错误MongoCommandException

Question

刚开始使用MongoDB。但是我收到错误，这对我来说毫无意义（来自SQL Server）。你能帮我理解造成这个问题的原因吗？

30440 2015:12:15 05:09:19 ERROR Application error.
Exception: MongoDB.Driver.MongoCommandException
Message: Command 'update' failed: not master (response: { "note" : "from execCommand", "ok" : 0.0, "errmsg" : "not master" })
Source: MongoDB.Driver
   at MongoDB.Driver.Operations.CommandOperation`1.Execute(MongoConnection connection)
   at MongoDB.Driver.Operations.BulkUnmixedWriteOperationBase.ExecuteBatch(MongoConnection connection, Batch`1 batch, Int32 originalIndex)
   at MongoDB.Driver.Operations.BulkUnmixedWriteOperationBase.Execute(MongoConnection connection)
   at MongoDB.Driver.Operations.BulkUpdateOperation.Execute(MongoConnection connection)
   at MongoDB.Driver.Operations.UpdateOpcodeOperationEmulator.Execute(MongoConnection connection)
   at MongoDB.Driver.Operations.UpdateOpcodeOperation.Execute(MongoConnection connection)
   at MongoDB.Driver.MongoCollection.Update(IMongoQuery query, IMongoUpdate update, MongoUpdateOptions options)
   at MongoDB.Driver.MongoCollection.Update(IMongoQuery query, IMongoUpdate update, UpdateFlags flags, WriteConcern writeConcern)
   at Sitecore.SessionProvider.MongoDB.MongoSessionStateStore.InsertItem(String application, String id, Int32 flags, SessionStateStoreData sessionState)
   at Sitecore.SessionProvider.MongoDB.SimpleMongoSessionStateStore.InsertItem(String application, String id, Int32 flags, SessionStateStoreData sessionState)
   at Sitecore.SessionProvider.MongoDB.MongoSessionStateProvider.SetAndReleaseItemExclusive(HttpContext context, String id, SessionStateStoreData sessionState, Object lockId, Boolean newItem)
   at System.Web.SessionState.SessionStateModule.OnReleaseState(Object source, EventArgs eventArgs)
   at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)