[flexcoders] mx.rpc.soap::Operation::invokePending error

[nehavyas13]

I am trying to access a wsdl file and getting following error. Can
somebody please help me and tell me what this error means and how can
I find out what null is?

Thanks in advance

[RPC Fault faultString="Error #1009: Cannot access a property or
method of a null object reference." faultCode="EncodingError"
faultDetail="null"]
        at
mx.rpc.soap::Operation/http://www.adobe.com/2006/flex/mx/internal::invokePendingCall()[E:\dev\3.0.x\frameworks\projects\rpc\src\mx\rpc\soap\Operation.as:774]
        at
mx.rpc.soap::Operation/send()[E:\dev\3.0.x\frameworks\projects\rpc\src\mx\rpc\soap\Operation.as:688]
        at Function/http://adobe.com/AS3/2006/builtin::apply()
        at
mx.rpc.soap.mxml::Operation/send()[E:\dev\3.0.x\frameworks\projects\rpc\src\mx\rpc\soap\mxml\Operation.as:167]
        at Function/http://adobe.com/AS3/2006/builtin::apply()
        at
mx.rpc::AbstractService/http://www.adobe.com/2006/actionscript/flash/proxy::callProperty()[E:\dev\3.0.x\frameworks\projects\rpc\src\mx\rpc\AbstractService.as:285]
        at
MonitoringStats/___MonitoringStats_Button4_click()[C:\Projects\mailroomStatistics\src\flex\MonitoringStats\MonitoringStats.mxml:243]