Cannot send Direct message to my friend

[sovannarithsok]

Accordance with "http://api.t.sina.com.cn/direct_messages/new.json?" that need some parameter such as: source, id, text, user_id, screen_name. I always receive error as below:
{"request":"/1/direct_messages/new.json","error_code":"403","error":"40302:auth by Null spi!"}

What's the problem?