This error was resulted in a specific scenario where I tried to pull a service metadata using .NET MetadataExchangeClient.
The reason was that the metadata consisted with more metadata references than the limit defined on my MEXClient instance. (The default is 10)
Solution - Increase the limit.
MetadataExchangeClient mexClient = new MetadataExchangeClient();
mexClient.MaximumResolvedReferences = MaximumResolvedReferences; //some constant