problem finding synonym in NHunpell

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C#

ASP.NET

here is my code

MyThes thes = new MyThes("th_en_us_new.idx", "th_en_us_new.dat");

Hunspell hunspell = new Hunspell("en_us.aff", "en_us.dic");

ThesResult tr = thes.Lookup("country", hunspell);

Response.Write(tr.IsGenerated.ToString());

now the problem is tr.IsGenerated is always false no matter what string i give as an input....
can any one help...