Hi plevintampabay!
The parameter is case-sensitive, as all parameters in the locator string are. Note that the value is not in this case, so any of "true", "TRUE", or "TrUe" are all valid.
However that isn't the problem here, obviously 
I assume you've read Everything You Need To Know About Simultaneous Record and Playback on CDMA Devices, since it's also posted almost verbatim earlier in this thread...
Here is code I've used to test this *successfully* just now on my Style using the same build 6.0.0.524:
FileConnection file = null;
InputStream fileInputStream = null;
try {
// Recorder
recorder = javax.microedition.media.Manager.createPlayer("capture://audio?encoding=audio/amr&bitrate=12200&voip Mode=true");
recorder.addPlayerListener( ... );
recorder.realize();
recordControl = (RecordControl) recorder.getControl( "RecordControl" );
recordControl.setRecordLocation( "file:///SDCard/path/to/filename.amr");
// Player
file = (FileConnection) Connector.open(playbackFilename);
fileInputStream = file.openInputStream();
player = javax.microedition.media.Manager.createPlayer( fileInputStream, "audio/amr" );
player.addPlayerListener( ... );
// Start order matters here -> start recorder first
recordControl.startRecord();
recorder.start();
player.start();
} catch (Exception e) {
// Error handling here
}
It's simplified a bit so it's easier to understand. Note that the source of the player media must be a stream (it cannot be a file URL) so I cheated a bit and used an InputStream to a file. Where the data is recorded to doesn't matter, I used a file here but it could easily have been a stream as well.
The logs you provided shows that the recorder is stopped before the player even starts due to preemption, presumably from the playback player as you suspect.
I've done all I can with what you've given me here, if this doesn't help please post some code!
EDIT: Fixed some typos.
