SignalR + Redis backplane = System.InvalidOperationException: The queue is full

Question

I use SignalR with redis backplane. To set up it, I use simple code

var redisConfig = new RedisScaleoutConfiguration("connectionString","eventKey");
GlobalHost.DependencyResolver.UseRedis(redisConfig);

Everything worked fine,but than I began to get following exceptions.

Unhandled exception in Portal UI:System.InvalidOperationException: The queue is full. at Microsoft.AspNet.SignalR.Messaging.ScaleoutStream.Send(Func2 send, Object state) at Microsoft.AspNet.SignalR.Infrastructure.Connection.Send(ConnectionMessage message) at Microsoft.AspNet.SignalR.Transports.TransportConnectionExtensions.SendCommand(ITransportConnection connection, String connectionId, CommandType commandType) at Microsoft.AspNet.SignalR.Transports.ForeverTransport.ProcessRequestCore(ITransportConnection connection) at Microsoft.AspNet.SignalR.PersistentConnection.ProcessRequestPostGroupRead(HostContext context, String groupsToken) at Microsoft.AspNet.SignalR.TaskAsyncHelper.FromMethod[T1,T2,T3,TResult](Func4 func, T1 arg1, T2 arg2, T3 arg3) --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.Owin.Mapping.MapMiddleware.d__0.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContextStage.d__5.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.Owin.Security.Infrastructure.AuthenticationMiddleware1.<Invoke>d__0.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.Owin.Security.Infrastructure.AuthenticationMiddleware1.d__0.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContextStage.d__5.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.d__2.MoveNext() --- End of stack trace from previous location where exception was thrown --- at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.StageAsyncResult.End(IAsyncResult ar) at System.Web.HttpApplication.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

I looked into redis cache . It seems that it's ok. It has enough space.

What doest 'The queue is full' mean? What is this queue? How can I avoid such exceptions?