프로그램 실행 에러

OnRecvCompleted Failed System.InvalidOperationException: Collection was modified; enumeration operation may not execute.   at System.Collections.Generic.List`1.Enumerator.MoveNextRare()

   at Server.GameRoom.Broadcast(ClientSession session, String chat) in C:\Users\lll\source\repos\Server\Server\GameRoom.cs:line 27

   at PacketHandler.C_ChatHandler(PacketSession session, IPacket packet) in C:\Users\lll\source\repos\Server\Server\Packet\PacketHandler.cs:line 19

   at PacketManager.MakePacket[T](PacketSession session, ArraySegment`1 buffer) in C:\Users\lll\source\repos\Server\Server\Packet\ServerPacketManager.cs:line 58

   at PacketManager.OnRecvPacket(PacketSession session, ArraySegment`1 buffer) in C:\Users\lll\source\repos\Server\Server\Packet\ServerPacketManager.cs:line 42

   at Server.ClientSession.OnRecvPacket(ArraySegment`1 buffer) in C:\Users\lll\source\repos\Server\Server\Session\ClientSession.cs:line 30

   at ServerCore.PacketSession.OnRecv(ArraySegment`1 buffer) in C:\Users\lll\source\repos\Server\ServerCore\Session.cs:line 34

   at ServerCore.Session.OnRecvCompleted(Object sender, SocketAsyncEventArgs args) in C:\Users\lll\source\repos\Server\ServerCore\Session.cs:line 214

안녕하세요

위와 같은 에러가 나왔는데, 아무래도 뭔가 제가 코딩하면서 잘못 작성한 부분이 잇는거겠죠? ㅎㅎ ㅠㅠ

문서 찾아보니 아래와 같이 나오네요. foreach  문 안에서는 컬렉션에 수정을 하면 안된다?  같네요..

https://docs.microsoft.com/ko-kr/dotnet/api/system.invalidoperationexception?view=net-6.0#Iterating

foreach 구문을 고치라는데..정작 강의에서는 foreach 로 되어있어 난감하네요

코드비교를 해봐도..어느부분이 문제인지 알수가 없어 일단 다음 강의로넘어갑니다ㅠㅠ