GdataRequestException

Question

GdataRequestException was unhandled by user code
and The remote server returned an error: (400) Bad Request.
I have no of question like
1-Please tell me how can i solve my Above problem  
2-Is YOUTUBE_DEVELOPER_KEY also known as API ..?
3-what should i use over here in Empty " ? "..? I am using my youtube channel name ... like- "xyz chennal "  it is right ..?


YouTubeRequestSettings settings = new YouTubeRequestSettings(" ? ", YOUTUBE_DEVELOPER_KEY); 

Pleas solve my problm each and every time i stuck over here ..