Impossible to route: org.mule.transport.amqp.AmqpMessage - rabbitmq

Question

I'm having a random problem with amqp components in Mule.
This is the scenario:
I set a global AMQP connector to be used for both Mule Flows
<amqp:connector
name="amqpLocalhostConnector"
host="${amqp.host}"
port="${amqp.port}"
fallbackAddresses="${amqp.fallbackAddresses}"
virtualHost="${amqp.virtualHost}"
username="${amqp.username}"
password="${amqp.password}"
ackMode="MANUAL"
prefetchCount="1" />
This flows sends a notification to RabbitMQ
<flow
name="notifyRabbitMQ"
doc:name="notifyRabbitMQ">
<!-- Set the payload with an ID from an element in a database -->
<set-payload
doc:name="Set Payload"
value="123abc"/>
<!-- Send the ID into an amqp message to RabbitMQ -->
<amqp:outbound-endpoint
exchangeName="exchange"
routingKey="file.id"
connector-ref="amqpLocalhostConnector">
</amqp:outbound-endpoint>
</flow>
This flow gets the notification from the RabbitMQ queue and then process it.
<flow
name="processNotification"
doc:name="processNotification"
processingStrategy="synchronous">
<amqp:inbound-endpoint
queueName="files"
connector-ref="amqpLocalhostConnector" />
<byte-array-to-string-transformer doc:name="Message to String (ID)"/>
<set-payload
value="#[app.registry.customFileService.findFile(payload)]"
doc:name="Get File" />
<logger message="SUCCESS!" level="INFO" doc:name="Logger"/>
<amqp:acknowledge-message />
</flow>
When I run the project, sometimes it works fine and sometimes it throws the following error:
ERROR 2015-07-17 12:37:47,620 [[rabbit_notification].amqpLocalhostConnector.receiver.01] org.mule.transport.amqp.AmqpMessageReceiver$AmqpMessageRouterWork: Impossible to route: org.mule.transport.amqp.AmqpMessage#43cac8[consumerTag=amq.ctag-jASX98hPWb7UUiIVHLOeEQ,envelope=Envelope(deliveryTag=2, redeliver=false, exchange=exchange, routingKey=file.id),body={53,53,97,57,50,49,52,98,50,50,50,57,101,56,56,51,55,101,98,54,102,100,56,53},properties=#contentHeader(content-type=null, content-encoding=UTF-8, headers={MULE_SESSION=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, MULE_ENCODING=UTF-8, MULE_ROOT_MESSAGE_ID=c628f745-2c99-11e5-b27a-e1c8fbc553ca, MULE_ENDPOINT=amqp://exchange}, delivery-mode=2, priority=0, correlation-id=null, reply-to=null, expiration=null, message-id=c628f745-2c99-11e5-b27a-e1c8fbc553ca, timestamp=Fri Jul 17 12:37:47 ART 2015, type=null, user-id=null, app-id=null, cluster-id=null)]
Does anyone knows why this could be happening?
Thanks in advance.