QueryFailure flag was unrecognized command: $query (response was { "$err" : "unrecognized command: $query", "code" : 13390 }).

   at MongoDB.Driver.Internal.MongoReplyMessage`1.ReadFrom(BsonBuffer buffer, IBsonSerializationOptions serializationOptions) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Internal\MongoReplyMessage.cs:line 99
   at MongoDB.Driver.Internal.MongoConnection.ReceiveMessage[TDocument](BsonBinaryReaderSettings readerSettings, IBsonSerializationOptions serializationOptions) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Internal\MongoConnection.cs:line 475
   at MongoDB.Driver.MongoCursorEnumerator`1.GetReply(MongoConnection connection, MongoRequestMessage message) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoCursorEnumerator.cs:line 296
   at MongoDB.Driver.MongoCursorEnumerator`1.GetFirst() in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoCursorEnumerator.cs:line 253
   at MongoDB.Driver.MongoCursorEnumerator`1.MoveNext() in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoCursorEnumerator.cs:line 141
   at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
   at MongoDB.Driver.MongoCollection.FindOneAs[TDocument](IMongoQuery query) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoCollection.cs:line 557
   at MongoDB.Driver.MongoCollection`1.FindOne(IMongoQuery query) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoCollection.cs:line 1734
   at MongoDB.Driver.MongoDatabase.RunCommandAs(Type commandResultType, IMongoCommand command) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoDatabase.cs:line 973
   at MongoDB.Driver.MongoDatabase.RunCommandAs[TCommandResult](IMongoCommand command) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoDatabase.cs:line 950
   at MongoDB.Driver.MongoCollection.Aggregate(IEnumerable`1 operations) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoCollection.cs:line 124
   at MongoDB.Driver.MongoCollection.Aggregate(BsonDocument[] operations) in D:\Temp\mongodb-code\mongodb-mongo-csharp-driver-98a0129\Driver\Core\MongoCollection.cs:line 134
   at TopSecretProject;).Service.Internal.AggregateFramework.BaseAggregateFrameworkMongoMentionService.GetAggregateResult(MentionAggregateQuery query, MongoField groupingKey, IDictionary`2 includeAggregateFields, BsonDocument[]& commands, Boolean isTimeSeries) in D:\Projects\TopSecretProject;)\Service\Internal\AggregateFramework\BaseAggregateFrameworkMongoMentionService.cs:line 50
   at TopSecretProject;).Service.Internal.AggregateFramework.AggregateFrameworkMongoMentionService.GetTopItemResults(MentionAggregateQuery query, IDictionary`2 includeAggregateFields) in D:\Projects\TopSecretProject;)\Service\Internal\AggregateFramework\AggregateFrameworkMongoMentionService.cs:line 22

MongoDB.Driver: C# 1.6.1.20900
MongoDB.Bson: C# 1.6.1.20899
Mongos: 2.07
- 1 master set (3 shards) 2.07
- 1 slave set (3 shards) 2.2
connectionString: mongodb://mongos-version-2.0.7-ip:port/?readPreference=secondaryPreferred