An AIR application I am working on makes a single call to two separate services. I get the following error: PHP Fatal error: Uncaught exception 'Zend_Amf_Exception' with message 'Unable to parse null body data Unsupported type marker: 36' in /var/www/lib/Zend/Amf/Request.php:174 Stack trace: #0 /var/www/lib/Zend/Amf/Request.php(125): Zend_Amf_Request->readBody() #1 /var/www/lib/Zend/Amf/Request.php(93): Zend_Amf_Request->readMessage(Object(Zend_Amf_Parse_InputStream)) #2 /var/www/lib/Zend/Amf/Request/Http.php(64): Zend_Amf_Request->initialize('??????null/...') #3 /var/www/lib/Zend/Amf/Server.php(365): Zend_Amf_Request_Http->__construct() #4 /var/www/lib/Zend/Amf/Server.php(313): Zend_Amf_Server->getRequest() #5 /var/www/index.php(26): Zend_Amf_Server->handle() #6 {main} thrown in /var/www/lib/Zend/Amf/Request.php on line 174 I'm using the Cairngorm framework, and the following two events, which result in requests to Zend AMF, cause this error to occur: new DataSetEvent(DataSetEvent.GET_ALL).dispatch(); new SPIChartEvent().dispatch(); If I comment out either line so that only one request is sent at a time, the issue does not appear. Similarly, if I change the RemoteObject in my service locator from this: <mx:RemoteObject id="DataSetService" destination="zend" source="DataSetService" showBusyCursor="true" /> to this: <mx:RemoteObject id="DataSetService" destination="zend" source="DataSetService" showBusyCursor="true" concurrency="single" /> the issue is again avoided. I am guessing that Flash is pipelining the calls into a single request and Zend's parser isn't expecting this. Not sure, I'm not an expert in AMF, just my guess.