It's not a bug. Sometimes, if the authentication mode is goofed up (it's just a configuration in the registry) by the sys admin people.
Your sql server won't be part of all the three modes of authentication.
This option is used to find the same.
Thanks to all for your precious time. By next week, I will write a detailed article in my blog.
Venkatesan Prabu .J
Thanks and Regards,