hey my game keeps crashign when im in cooapertive mode and I get this error

Build AmericasArmy[BuildDate:03-15-07_BuildVersion:2.8.1]

OS: Windows XP 5.1 (Build: 2600)
CPU: GenuineIntel Unknown processor @ 3195 MHz with 1022MB RAM
Video: NVIDIA GeForce FX 5200 (6218)

IDirect3DVertexBuffer8::Lock failed(D3DERR_NOTAVAILABLE).

History: FSkinVertexStream::GetStreamData <- FALVoiceModule::NoteDestroy <- UALAudioSubsystem::NoteDetroy <- ULevel:estroyActor <- (M83SmokeEmitter interdiction.M83SmokeEmitter) <- UObject::ProcessEvent <- (HumanController interdiction.HumanController, Function AGP.HumanController.Spectating.EndState) <- ULevel:estroyActor <- (HumanController interdiction.HumanController) <- UPlayer:estroy <- UViewport:estroy <- (WindowsViewport Package.WindowsClient.WindowsViewport) <- UWindowsViewport:estroy <- UObject::ConditionalDestroy <- (WindowsViewport Package.WindowsClient.WindowsViewport) <- UWindowsClient::Tick <- ClientTick <- UGameEngine::Tick <- Level Interdiction <- UpdateWorld <- MainLoop