Hello, I posted about this issue a week ago, and Ian was kind enough to explain this to me. Search the maillist for “Managed ESL: AccessViolationException”. In short, yes, accessing the same eslConnection from multiple threads causes this exception. I created a single object which listens for all the events and sends them to all other objects which subscribe to receive events. This way you have only 1 thread listening for events on the socket, and can have multiple threads processing the events. I believe you can send and receive on the same socket from 1 thread, since .net sockets are bi-directional. From: freeswitch-users-bounces@lists.freeswitch.org [mailto:freeswitch-users-bounces@lists.freeswitch.org] On Behalf Of Ferenc Sárközy Sent: Thursday, May 29, 2014 4:40 PM To: FreeSWITCH Users Help Subject: [Freeswitch-users] ESL C# Accessviolation Hi, My C# app uses ESL to interact with FS. It plays wav files via bgapi and receives and processes the events of the playbacks. The listening thread is started like ManagedESLTest program: ThreadPool.QueueUserWorkItem(new WaitCallback(getFsEventsInboundMode)); this thread ends up in a while loop where the events are received: while (eslConnection.Connected() == ESL_SUCCESS && !stopConnection) { eslEvent = eslConnection.RecvEventTimed(50); if (eslEvent != null) { onFreeswitcEvent(eslEvent ); } } onFreeSwitchEvent calls ends up in an other thread. bgapi commands is sent via the same eslConnection, I assume that the occasional Accessviolation at RecvEventTimed is caused by sending bgapi commands via the same eslConnection from an other thread. Could that be the cause? Other related questions: Is it safe to pass eslEvent to an other thread, or it should be serialized? If so is there a best practice to serialize? Is there some kind of event buffer in eslConnection, or the RecvEvent misses all the events which "arrived" before the call? Thank you in advance: Ferenc