Is there any limitation on the frequency of writing to MSMQ?

I have a long running process which writes some status messages to msmq. i also have a configuration value which limits the number of message generated by long running process. the code works fine when i use the limit and only write 1/50 of the generated messages to the queue. my code crashes with an access violation exception when the frequency by which I call MSMQEnqueue increases.

the exception is:

First-chance exception at 0x000007fef2096a15 in w3wp.exe: 0xC0000005: Access violation reading location 0x0000000000000000.

does any body know what the limitation could be?

// Retrieves or Creates private queues with the key and sends a message to it
        public void MSMQEnqueue(string sKey, string sMessage)
        {
            MessageQueue queue = GetOrCreateQueue(sKey);
            try
            {
                Message message = new Message();
                message.Body = sMessage;

                queue.Purge();
                queue.Send(message);
            }

            finally {
                queue.Dispose();

            }

        }

            // Retrieves or Creates private queues with a key 
        public MessageQueue GetOrCreateQueue(string sKey)
        {
            MessageQueue queue;
            // Create and connect to a private Message Queuing queue.
            if (!MessageQueue.Exists(string.Format(".\\Private$\\{0}", sKey)))
            {
                // Create the queue if it does not exist.
                queue = MessageQueue.Create(string.Format(".\\Private$\\{0}", sKey));
            }

            else
            {
                queue = new MessageQueue(string.Format(".\\Private$\\{0}", sKey));
            }

            queue.Formatter = new XmlMessageFormatter(new String[] { "System.String,mscorlib" });
            queue.MessageReadPropertyFilter.SetAll();

            return queue;
        }