microsoft/autogen · error · ArgumentException

System message is not supported when message.From is the sam

Error message

System message is not supported when message.From is the same with agent

What it means

In the own-message branch (message.From == agent.Name) of the deprecated conversion, a TextMessage with Role.System throws. Messages attributed to the agent map to ChatRequestAssistantMessage; an assistant-role slot cannot carry a system prompt, so the combination is rejected instead of silently mislabeling it.

Source

Thrown at dotnet/src/AutoGen.OpenAI.V1/Extension/MessageExtension.cs:161

                }
                else
                {
                    var userMessage = new ChatRequestUserMessage(msg.Content ?? throw new ArgumentException("Content is null"));
                    return [userMessage];
                }
            }
            else
            {
                throw new ArgumentException($"Unknown message type: {message.GetType()}");
            }
        }
        else
        {
            if (message is TextMessage textMessage)
            {
                if (textMessage.Role == Role.System)
                {
                    throw new ArgumentException("System message is not supported when message.From is the same with agent");
                }

                return [new ChatRequestAssistantMessage(textMessage.Content)];
            }
            else if (message is ToolCallMessage toolCallMessage)
            {
                var assistantMessage = new ChatRequestAssistantMessage(string.Empty);
                var toolCalls = toolCallMessage.ToolCalls.Select(tc => new ChatCompletionsFunctionToolCall(tc.FunctionName, tc.FunctionName, tc.FunctionArguments));
                foreach (var tc in toolCalls)
                {
                    assistantMessage.ToolCalls.Add(tc);
                }

                return [assistantMessage];
            }
            else if (message is AggregateMessage<ToolCallMessage, ToolCallResultMessage> aggregateMessage)
            {
                var toolCallMessage1 = aggregateMessage.Message1;

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Keep system prompts out of the replayed history; supply them via systemMessage at agent construction
2. When echoing history, set From = null (or the true sender) for system-role messages
3. Filter Role.System messages out of anything you forward back to the agent

Example fix

// before
var replayed = new TextMessage(Role.System, systemPrompt, from: agent.Name);
await agent.SendAsync(replayed);

// after
// system prompt handled at construction:
var agent = new OpenAIChatAgent(client, "gpt", options, systemMessage: systemPrompt);
// history replay contains only user/assistant messages

bool ok = textMsg.Role != Role.System || textMsg.From != agent.Name;
if (!ok) textMsg = new TextMessage(Role.User, textMsg.Content, from: null);

static bool IsOwnSystemMessage(TextMessage m, string agentName) =>
    m.Role == Role.System && m.From == agent.Name;

catch (ArgumentException ex) when (ex.Message.Contains("System message is not supported"))
{
    var demoted = new TextMessage(Role.User, textMsg.Content, from: null);
    return await agent.SendAsync(demoted);
}

When it happens

Trigger: Replaying a system message whose From was set to the agent's name (e.g. echoing the whole conversation, including the system turn, back with From rewritten) into the same agent.

Common situations: History replay loops that stamp From = agent.Name on every prior turn; copying the agent's system message into the chat as a TextMessage and then attributing it to the agent.

Related errors

• Multiple and Not continuous system messages are not supporte
• Failed to fetch galleries
• Failed to fetch gallery
• Please set OPENAI_API_KEY environment variable.
• Please set OPENAI_API_KEY environment variable.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/5bd2aed7954cf4e5. Report an issue: GitHub.