AUGraphInitialize an error code -10868 when adding kAudioUnitSubType_Reverb2 to AUGraph

I'm attempting to add an AudioUnit of type kAudioUnitSubType_Reverb2 to an AUGraph and am getting a -10868 (kAudioUnitErr_FormatNotSupported) supported error on AUGraphInitialize. My starting point was Apple's iPhoneMixerEQGraphTest sample app, I've basically just added a new AudioUnit for the reverb but cannot get it to work.

Here is the code -

- (void)initializeAUGraph
 {
     printf("initializeAUGraph\n");
 
     AUNode outputNode;
     AUNode eqNode;
     AUNode mixerNode;
     AUNode reverbNode;
 
     printf("create client ASBD\n");
 
     // client format audio goes into the mixer
     mClientFormat.SetCanonical(2, true);                        
     mClientFormat.mSampleRate = kGraphSampleRate;
     mClientFormat.Print();
 
     printf("create output ASBD\n");
 
     // output format
     mOutputFormat.SetAUCanonical(2, false);                     
     mOutputFormat.mSampleRate = kGraphSampleRate;
     mOutputFormat.Print();
 
     OSStatus result = noErr;
 
     // load up the audio data
     [self performSelectorInBackground:@selector(loadFiles) withObject:nil];
 
     printf("new AUGraph\n");
 
     // create a new AUGraph
     result = NewAUGraph(&mGraph);
     if (result) { printf("NewAUGraph result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     // create three CAComponentDescription for the AUs we want in the graph
 
     // output unit
     CAComponentDescription output_desc(kAudioUnitType_Output, kAudioUnitSubType_RemoteIO, kAudioUnitManufacturer_Apple);
 
     // iPodEQ unit
     CAComponentDescription eq_desc(kAudioUnitType_Effect, kAudioUnitSubType_AUiPodEQ, kAudioUnitManufacturer_Apple);
 
     // multichannel mixer unit
     CAComponentDescription mixer_desc(kAudioUnitType_Mixer, kAudioUnitSubType_MultiChannelMixer, kAudioUnitManufacturer_Apple);
 
     // reverb unit
     CAComponentDescription reverb_desc(kAudioUnitType_Effect, kAudioUnitSubType_Reverb2, kAudioUnitManufacturer_Apple);
 
     printf("add nodes\n");
 
     // create a node in the graph that is an AudioUnit, using the supplied AudioComponentDescription to find and open that unit
     result = AUGraphAddNode(mGraph, &output_desc, &outputNode);
     if (result) { printf("AUGraphNewNode 1 result %lu %4.4s\n", result, (char*)&result); return; }
 
     result = AUGraphAddNode(mGraph, &eq_desc, &eqNode);
     if (result) { printf("AUGraphNewNode 2 result %lu %4.4s\n", result, (char*)&result); return; }
 
     result = AUGraphAddNode(mGraph, &mixer_desc, &mixerNode);
     if (result) { printf("AUGraphNewNode 3 result %lu %4.4s\n", result, (char*)&result); return; }
 
     result = AUGraphAddNode(mGraph, &reverb_desc, &reverbNode);
     if (result) { printf("AUGraphNewNode 4 result %lu %4.4s\n", result, (char*)&result); return; }
 
     // connect a node's output to a node's input
     // mixer -> eq -> output
     result = AUGraphConnectNodeInput(mGraph, mixerNode, 0, eqNode, 0);
     if (result) { printf("AUGraphConnectNodeInput result %lu %4.4s\n", result, (char*)&result); return; }
 
     result = AUGraphConnectNodeInput(mGraph, eqNode, 0, reverbNode, 0);
     if (result) { printf("AUGraphConnectNodeInput result %lu %4.4s\n", result, (char*)&result); return; }
 
     result = AUGraphConnectNodeInput(mGraph, reverbNode, 0, outputNode, 0);
     if (result) { printf("AUGraphConnectNodeInput reverb result %lu %4.4s\n", result, (char*)&result); return; }
 
     // open the graph AudioUnits are open but not initialized (no resource allocation occurs here)
     result = AUGraphOpen(mGraph);
     if (result) { printf("AUGraphOpen result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     // grab the audio unit instances from the nodes
     result = AUGraphNodeInfo(mGraph, mixerNode, NULL, &mMixer);
     if (result) { printf("AUGraphNodeInfo result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     result = AUGraphNodeInfo(mGraph, eqNode, NULL, &mEQ);
     if (result) { printf("AUGraphNodeInfo result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     result = AUGraphNodeInfo(mGraph, reverbNode, NULL, &mReverb);
     if (result) { printf("AUGraphNodeInfo reverb result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     // set bus count
     UInt32 numbuses = 2;
 
     printf("set input bus count %lu\n", numbuses);
 
     result = AudioUnitSetProperty(mMixer, kAudioUnitProperty_ElementCount, kAudioUnitScope_Input, 0, &numbuses, sizeof(numbuses));
     if (result) { printf("AudioUnitSetProperty result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     for (int i = 0; i < numbuses; ++i) {
         // setup render callback struct
         AURenderCallbackStruct rcbs;
         rcbs.inputProc = &renderInput;
         rcbs.inputProcRefCon = &mUserData;
 
         printf("set AUGraphSetNodeInputCallback\n");
 
         // set a callback for the specified node's specified input
         result = AUGraphSetNodeInputCallback(mGraph, mixerNode, i, &rcbs);
         if (result) { printf("AUGraphSetNodeInputCallback result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
         printf("set input bus %d, client kAudioUnitProperty_StreamFormat\n", i);
 
         // set the input stream format, this is the format of the audio for mixer input
         result = AudioUnitSetProperty(mMixer, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, i, &mClientFormat, sizeof(mClientFormat));
         if (result) { printf("AudioUnitSetProperty result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
     }
 
     printf("get EQ kAudioUnitProperty_FactoryPresets\n");
 
     // get the eq's factory preset list -- this is a read-only CFArray array of AUPreset structures
     // host owns the retuned array and should release it when no longer needed
     UInt32 size = sizeof(mEQPresetsArray);
     result = AudioUnitGetProperty(mEQ, kAudioUnitProperty_FactoryPresets, kAudioUnitScope_Global, 0, &mEQPresetsArray, &size);
     if (result) { printf("AudioUnitGetProperty result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     /* this code can be used if you're interested in dumping out the preset list
     printf("iPodEQ Factory Preset List:\n");
     UInt8 count = CFArrayGetCount(mEQPresetsArray);
     for (int i = 0; i < count; ++i) {
         AUPreset *aPreset = (AUPreset*)CFArrayGetValueAtIndex(mEQPresetsArray, i);
         CFShow(aPreset->presetName);
     }*/
 
     printf("set output kAudioUnitProperty_StreamFormat\n");
 
     // set the output stream format of the mixer
     result = AudioUnitSetProperty(mMixer, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &mOutputFormat, sizeof(mOutputFormat));
     if (result) { printf("AudioUnitSetProperty result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     printf("set render notification\n");
 
     // add a render notification, this is a callback that the graph will call every time the graph renders
     // the callback will be called once before the graph's render operation, and once after the render operation is complete
     result = AUGraphAddRenderNotify(mGraph, renderNotification, &mUserData);
     if (result) { printf("AUGraphAddRenderNotify result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
 
     printf("AUGraphInitialize\n");
 
     // now that we've set everything up we can initialize the graph, this will also validate the connections
     result = AUGraphInitialize(mGraph);
     if (result) { printf("AUGraphInitialize result %ld %08X %4.4s\n", result, (unsigned int)result, (char*)&result); return; }
     // ---- result here is error code 10868
 
     CAShow(mGraph);
 }
 

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