No thumbnail generate

Hi
I download latest release of fckeditor for ASP.NET. it;s working fine using built in VS 2008 (I could upload/Rename/ ..) but the issue is that I can't see thumbs . instead of thumbs I see Pink question Mark
http://www.iimmgg.com/image/c359b5b030d ... 798370f60d

I noticed that it does not generate thumnail files ." _thumbs" folder exist and this is my setting

Thumbnails.Url = BaseUrl + "_thumbs/";
Thumbnails.Dir = BaseDir + "_thumbs/";
Thumbnails.Enabled = true;
Thumbnails.DirectAccess = false;
Thumbnails.MaxWidth = 100;
Thumbnails.MaxHeight = 100;
Thumbnails.Quality = 80;