You get this type of error because of the way Wowza module methods are invoked. It uses Java Reflection which does have the unwanted effect that any stack traces for uncaught exceptions will only go back as far as the invoke method. Unfortunately, the stack trace doesn't provide enough info to tell what caused the original exception.
To get the information you need, simply wrap the contents for your module methods with a try / catch block and log the exception. That exception should give you more information about the cause.
The original error tells you that the method that caused the exception was onHTTPCupertinoEncryptionKeyLiveChunk so use the following in that method
The log statement will log an error similar to what you are already getting but the difference is the stack trace will start from your method.
public void onHTTPCupertinoEncryptionKeyLiveChunk(ILiveStreamPacketizer liveStreamPacketizer, String streamName, CupertinoEncInfo encInfo, long chunkId, int mode)
// Put original method body here.
// Log exception and stack trace.
getLogger().error("onHTTPCupertinoEncryptionKeyLiveChunk Exception: " + e.getMessage(), e);
// Perform any cleanup here.