microsoft/autogen · error · NotImplementedException

The method or operation is not implemented.

Error message

The method or operation is not implemented.

What it means

NotImplementedException thrown while flattening a MultiModalMessage's content items: the connector only knows how to map TextMessage and ImageMessage items to ChatMessageContentItem. Any other IMessage inside the multimodal payload (e.g. a nested ToolCallMessage or custom type) hits the default switch arm.

Source

Thrown at dotnet/src/AutoGen.OpenAI.V1/Middleware/OpenAIChatRequestMessageConnector.cs:316

        }

        var imageContentItem = this.CreateChatMessageImageContentItemFromImageMessage(message);
        return [new ChatRequestUserMessage([imageContentItem]) { Name = message.From }];
    }

    private IEnumerable<ChatRequestMessage> ProcessMultiModalMessage(IAgent agent, MultiModalMessage message)
    {
        if (agent.Name == message.From)
        {
            // image message from assistant is not supported
            throw new ArgumentException("MultiModalMessage is not supported when message.From is the same with agent");
        }

        IEnumerable<ChatMessageContentItem> items = message.Content.Select<IMessage, ChatMessageContentItem>(ci => ci switch
        {
            TextMessage text => new ChatMessageTextContentItem(text.Content),
            ImageMessage image => this.CreateChatMessageImageContentItemFromImageMessage(image),
            _ => throw new NotImplementedException(),
        });

        return [new ChatRequestUserMessage(items) { Name = message.From }];
    }

    private ChatMessageImageContentItem CreateChatMessageImageContentItemFromImageMessage(ImageMessage message)
    {
        return message.Data is null && message.Url is not null
            ? new ChatMessageImageContentItem(new Uri(message.Url))
            : new ChatMessageImageContentItem(message.Data, message.Data?.MediaType);
    }

    private IEnumerable<ChatRequestMessage> ProcessToolCallMessage(IAgent agent, ToolCallMessage message)
    {
        if (message.From is not null && message.From != agent.Name)
        {
            throw new ArgumentException("ToolCallMessage is not supported when message.From is not the same with agent");
        }

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Ensure MultiModalMessage.Content contains only TextMessage and ImageMessage instances
2. Pull non-text/image items out and send them as separate messages
3. Catch NotImplementedException during prototyping to catch bad payload construction early

Example fix

// before
var mm = new MultiModalMessage(Role.User,
    new IMessage[] { text, new ToolCallMessage(...) }); // throws on process

// after
var mm = new MultiModalMessage(Role.User, new IMessage[] { text, image });
// send the tool call separately

bool valid = multiModal.Content.All(ci => ci is TextMessage or ImageMessage);
if (!valid) { /* strip unsupported items before sending */ }

static bool ContainsOnlySupportedItems(MultiModalMessage m) => m.Content.All(ci => ci is TextMessage or ImageMessage);

catch (NotImplementedException) { /* split multimodal payload into supported messages and resend */ }

When it happens

Trigger: Constructing new MultiModalMessage(Role.User, [textMessage, someOtherMessage]) where someOtherMessage is not TextMessage or ImageMessage, then sending it through the connector.

Common situations: Generic code that packages arbitrary message lists as multimodal content; future-proofing that assumed any IMessage could ride inside a multimodal message.

Related errors

• MultiModalMessage is not supported when message.From is the
• Please set AZURE_OPENAI_API_KEY environment variable.
• Please set AZURE_OPENAI_ENDPOINT environment variable.
• Please set environment variable AZURE_OPENAI_API_KEY
• Invalid aggregate message {reason}

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/88ec1945f77e2d46. Report an issue: GitHub.