"Method not found" error using .NET ease of use library to access LSEG's data platform

Our app uses the nuget package LSEG.Data to connect to Workspace and retrieve historical and realtime prices.
A customer recently upgraded to a new version of our app alongside the newest Workspace 1.26.602.
Since then, they cannot retrieve data anymore from Workspace. The RDP.log file contains a few suspicious entries:

2026-01-13T08:43:31 Info LSEG.Data.Delivery.Stream.OMMConnection Successfully connected into the WebSocket server: 127.0.0.1:9000/api/rdp/streaming/pricing/v1/WebSocket. Connection HashCode: 51781231 2026-01-13T08:43:31 Info LSEG.Data.Delivery.Stream.OMMConnection Session Event: StreamConnected 2026-01-13T08:43:31 Info LSEG.Data.Delivery.Stream.OMMConnection Sending login request to 127.0.0.1:9000/api/rdp/streaming/pricing/v1/WebSocket 2026-01-13T08:43:31 Info LSEG.Data.Delivery.Stream.OMMConnection Successfully logged into streaming server 127.0.0.1:9000/api/rdp/streaming/pricing/v1/WebSocket 2026-01-13T08:43:31 Info LSEG.Data.Delivery.Stream.OMMConnection Session Event: StreamAuthenticationSuccess 2026-01-13T08:43:32 Error LSEG.Data.Delivery.Stream.OMMConnection Application Exception in Refresh: Methode nicht gefunden: "System.String Newtonsoft.Json.Linq.JToken.ToString(Newtonsoft.Json.Formatting)". 2026-01-13T08:44:01 Error LSEG.Data.Delivery.Stream.OMMConnection Application Exception in Process Update: Methode nicht gefunden: "System.String Newtonsoft.Json.Linq.JToken.ToString(Newtonsoft.Json.Formatting)". 2026-01-13T08:45:01 Error LSEG.Data.Delivery.Stream.OMMConnection Application Exception in Process Update: Methode nicht gefunden: "System.String Newtonsoft.Json.Linq.JToken.ToString(Newtonsoft.Json.Formatting)". 2026-01-13T08:46:01 Error LSEG.Data.Delivery.Stream.OMMConnection Application Exception in Process Update: Methode nicht gefunden: "System.String Newtonsoft.Json.Linq.JToken.ToString(Newtonsoft.Json.Formatting)".

The German error message translates to "Method not found".

We are wondering what may cause this problem. We do use Newtonsoft.Json in our app as well and have a bindingRedirect set up to allow using the newest version (product version 13.0.4, assembly version 13.0.0.0) with transient dependencies from included components.

We cannot reproduce the customer's problem here in a clean environment.

Has anyone seen this error or knows what may actually cause this?

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Accepted answers

GoGoGroundhog

We have found the cause of the problem.
Our App is using the latest Newtonsoft.Json relase (v13.0.0.4).
The customer has installed an older version in their machine's Global Assembly Cache (GAC), v.13.0.0.3.
As both share the same assembly version (13.0.0.0), the system will pick the one from the GAC.
However the developers of Newtonsoft.Json implemented new changes which are incompatible with older versions. Changes like that must normally be indicated by increasing the assembly version.
This was unfortunately missed, see https://github.com/JamesNK/Newtonsoft.Json/issues/3084, which leads to the problem at hand.

Therefore, we are going to downgrade our App to the previous version 13.0.0.3, which will fix the customer's issue.

All comments

Jirapongse

@GoGoGroundhog

Thank you for reaching out to us.

It may be specific to the client's environment. We may need to verify the Newtonsoft version used in the client's environment. I found this discussion. The following code may be able to verify what the problem is.

using System;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

namespace NewtonsoftTest

{

    internal class Program

    {

        static void Main(string[] args)

        {

            Console.WriteLine("Hello, World!");

            var ass = typeof(JObject).Assembly;

            var assemblyInfo = ass;

            var assemblyLocation = ass.Location;

            Console.WriteLine(assemblyInfo);

            Console.WriteLine(assemblyLocation);


            string jsonString = "{\"Date\":\"2025-01-15T00:00:00-08:00\",\"TemperatureCelsius\":25,\"Summary\":\"Hot\"}";


            JToken parsed = JToken.Parse(jsonString);

            Console.WriteLine(parsed.ToString(Formatting.None));

        }

    }

}

wasin.w V3

Hello @GoGoGroundhog

According to https://www.nuget.org/packages/LSEG.Data#dependencies-body-tab on the NuGet repository website, the library needs Newtonsoft.Json version >= 13.0.3. If you have installed the LSEG.Data .NET library via NuGet, it should download the supported version for you.

Could you please verify your Newtonsoft.Json version and how did you install the library?

GoGoGroundhog

Therefore, we are going to downgrade our App to the previous version 13.0.0.3, which will fix the customer's issue.

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