TypeError: Error #1009: Cannot access a property or method of a null object reference.
at mx.data::ConcreteDataService/http://www.adobe.com/2006/flex/mx/internal::getDataListWithCollectionId()[C:\depot\flex\branches\enterprise_corfu_rc\frameworks\projects\data\src\mx\data\ConcreteDataService.as:2862]
at mx.data::ConcreteDataService/http://www.adobe.com/2006/flex/mx/internal::processUpdateCollection()[C:\depot\flex\branches\enterprise_corfu_rc\frameworks\projects\data\src\mx\data\ConcreteDataService.as:3611]
at mx.data::DataStore/http://www.adobe.com/2006/flex/mx/internal::commitResultHandler()[C:\depot\flex\branches\enterprise_corfu_rc\frameworks\projects\data\src\mx\data\DataStore.as:1625]
at mx.data::CommitResponder/result()[C:\depot\flex\branches\enterprise_corfu_rc\frameworks\projects\data\src\mx\data\CommitResponder.as:415]
at mx.rpc::AsyncRequest/acknowledge()[E:\dev\3.1.0\frameworks\projects\rpc\src\mx\rpc\AsyncRequest.as:74]
at NetConnectionMessageResponder/resultHandler()[E:\dev\3.1.0\frameworks\projects\rpc\src\mx\messaging\channels\NetConnectionChannel.as:491]
at mx.messaging::MessageResponder/result()[E:\dev\3.1.0\frameworks\projects\rpc\src\mx\messaging\MessageResponder.as:199]
I've lost so much time with this error. please help me