I use skype`s api ,use comman 'SET AUDIO_IN DeviceName',but retun code 50,set fail
i use device is USB Audio

When you change the device using the client to use this device and use a Get call, are you using that same devicename. Not sure if you understand what I mean, but, this would be a way to make sure what you are calling the device is actually what the device is known as, if you can query what it is called to compare what you are calling it, which maybe the problem, maybe you are not calling it but the right name?