OpenTK/OpenAL Alc.OpenDevice() - System.NullReferenceException

Device: Galaxy S4. I download last version monodroid(API Level 17, SDK 4.2), connected OpenTK from reference and add native library libopenal.so, set up dllmap

When I try to create AudioContext() var ac = new AudioContext(); - error - System.NullReferenceException: Object reference not set to an instance of an object

I downloaded the source code from https://github.com/mono/opentk and build it under monodroid, in result - error in line:

dummy_device = Alc.OpenDevice(null); - System.NullReferenceException: Object reference not set to an instance of an object What's the problem?

Thanks.