Add innerexception message in case of a fault

StackExchange.Redis/StackExchange/Redis/ConnectionMultiplexer.cs

@@ -762,7 +762,7 @@ public static ConnectionMultiplexer Connect(ConfigurationOptions configuration,
                         throw new TimeoutException();
                     }
                 }
-                if(!task.Result) throw ExceptionFactory.UnableToConnect();
+                if (!task.Result) throw ExceptionFactory.UnableToConnect(muxer.failureMessage);
                 killMe = null;
                 return muxer;
             }
@@ -772,6 +772,7 @@ public static ConnectionMultiplexer Connect(ConfigurationOptions configuration,
             }
         }
 
+        private string failureMessage;
         private readonly Hashtable servers = new Hashtable();
         private volatile ServerEndPoint[] serverSnapshot = NilServers;
 
@@ -1183,6 +1184,7 @@ internal async Task<bool> ReconfigureAsync(bool first, bool reconfigureAll, Text
                             foreach (var ex in aex.InnerExceptions)
                             {
                                 LogLocked(log, "{0} faulted: {1}", Format.ToString(endpoints[i]), ex.Message);
+                                failureMessage = ex.Message;
                             }
                         }
                         else if (task.IsCanceled)

StackExchange.Redis/StackExchange/Redis/ExceptionFactory.cs

@@ -106,10 +106,10 @@ static string GetLabel(bool includeDetail, RedisCommand command, Message message
             return message == null ? command.ToString() : (includeDetail ? message.CommandAndKey : message.Command.ToString());
         }
 
-        internal static Exception UnableToConnect()
+        internal static Exception UnableToConnect(string failureMessage=null)
         {
             return new RedisConnectionException(ConnectionFailureType.UnableToConnect,
-                "It was not possible to connect to the redis server(s); to create a disconnected multiplexer, disable AbortOnConnectFail");
+                "It was not possible to connect to the redis server(s); to create a disconnected multiplexer, disable AbortOnConnectFail. " + failureMessage);
         }
     }
 }