SMO : Full-text is not supported on this edition of SQL Server

See more:

C#

I have a problem with my sql server 2005.
I installed sql server 2005 Advanced service before implementing Fulltext search application.
Now in my application when i checked if Fulltextservice is installed on the server it return true,
but when i want to access the database fulltextcatalogs the application throws this exception:
"Full-text is not supported on this edition of SQL Server."

Although I implemented fulltext search and it works perfectly when i performed search in the application.
I wondering why the line throws exception.
I spent 2 days on this without finding solution.
this is my source code:

srv = new Server(_instancename)

if (srv.IsFullTextInstalled == true)//this line return true
{
 Database db = srv.Databases["jorce"];
 if (! db.FullTextCatalogs.Contains("JorceFTCat"))//this line throws exception: "Full-text is not supported on this edition of SQL Server."
 {
 FullTextCatalog ftc = new FullTextCatalog(db, "JorceFTCat");
 ftc.IsDefault = true;
 ftc.Create();
 }
}

I'm confused.
Thanks for the help.