Session with Forms authentication

[Salim Afþar]

Hi,
I use Forms Authentication type in my project.When I start my app. in the
browser it works well.First it redirects the login page and after I enter
the password it redirects my administration page(again it's OK).I get the
user details and add to Session object in login page and I get the details
in administration page from Session object:
string sUserType=Session["UserType"].ToString();

But if I try the same processes second time it displays an error like this:

System.NullReferenceException: Object reference not set to an instance of an
object.

string sUserType=Session["UserType"].ToString();

Any help will appreciated kindly.

Thanks a lot.

Salim