SystemError in Teams Group Chat for Copilot Studio Agent

The error code MCS-4041 with SystemError means the failure is happening inside the Copilot Studio service itself, not in your agent logic. Microsoft has not published that specific code publicly, which basically confirms it is a server side issue that their engineers need to trace on their end.

As for why it works for you in the group chat but not for the others, the most likely explanation is that when the new Copilot Studio UI publishes your agent to Teams, it generates an app manifest that does not always include the right permissions for other participants in a group chat to interact with it. You are fine because as the creator you have implicit access, but everyone else hits a wall when they try to send a message.

A quick thing to try first: go into your agent's Teams channel settings in Copilot Studio, toggle off "Use this for group and meeting chat", save, toggle it back on, and republish. This forces a fresh manifest to be generated. You can also ask the affected users to type /debug clearstate in the chat, which clears any stuck conversation state on their end.

If that does not fix it, the best move is to raise a support ticket through the Microsoft 365 admin center. Make sure to include the reference code MCS-4041, the conversation IDs from the affected users, and the exact times the errors happened. That reference code is what lets Microsoft support pull the right server side trace and actually get to the bottom of it rather than giving you the standard checklist.