Context.Session

Dear Friend,

I meet a strange situation about Session in C#

I am building a web service, and want to store my user name in session, however, i always get the exception:


I coded like:
Session["name"] = username;

Then, I did some testing like:

if(Context.Session == null)
{
return "null session";
}

I find that the session is null, then I checked msdn, I cannot find any resource to create a session , may I know there are any other way to initialize a session so that I can store value.

Thanks