Facebook web app session information missing

I made a really basic facebook app that collects permission from the user to post data. Some time ago (around New Years) everything worked fine. I am using http://facebooktoolkit.codeplex.com and my code looks like this:

public partial class Facebook : CanvasFBMLBasePage
{
   protected void Page_Load(object sender, EventArgs e)
   {
      if(this.Api.Users.HasAppPermission(global::Facebook.Schema.Enums.ExtendedPermissions.publish_stream))

      

        
        
        
      

    

And at the moment I have an exception: uid parameter or session key is required

As I understand it, I must have some sort of session defined by Facebook and CanvasFBMLBasePage must parse it and use it, but it doesn't.

My application settings (maybe I am something wrong):

• Canvas callback url: http://www.domain.com/app/action/facebook.aspx ?
• Render Method: FBML
• Also, I have whitelisted my IP address.

thanks for the help