When trying to send two or more requests at the same time on the same connection object, I receive a Client.Data.Underflow error for each request following the first one. This is the offending code:

        var responder:Responder= new Responder(this.handleUserFilters,Application.application.faultHandler);
        WebService.call("Web_Service_Model.getUserFilters",responder,filterID);

        var responder2:Responder=new Responder(handleFilterProperties,Application.application.faultHandler);
        WebService.call("Web_Service_model.getFilterProperties",responder2,filterID);

The second web service call will generate the error. I have been able to work around the issue by creating a function that makes a new NetConnection object for each call requested, however I know that AMF should be capable of handling simultaneous requests as I am coming over from AMFPHP where such a thing was possible.