Session value expires with custom membership provider

 Hi All,
I have created a custom membership provider where only applied the method ValidateUser. In the login page, if the login was successful, I store a value in the session. This value is required for the BLL. In some pages, I check for this session value in the page load event:
            Dim myValue As String = Session("someValue")
            If String.IsNullOrEmpty(myValue) Then
                  Response.Redirect("login.aspx")
            End If
 now on some occations, accessing these pages redirect me to the login page, even if accessed few seconds later.
 
Any Idea?
 
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