Illustrator SDK :: Not Able To Get Font Style For Some Fonts

I am getting font style(like regular, bold, italic etc) like this-
 
while (count < fontCount) {//loop , which iterate throgh used fonts.
                                                  ATE::IFont currentFont = fontRefArray.Item(count);
                                                  if (!currentFont.IsNull()) {
                                                            FontRef fontRef = currentFont.GetRef();
                                                            AIFontKey fontKey = NULL;
                                                            result = sAIFont->FontKeyFromFont(fontRef, &fontKey);
                                                            result = sAIFont->GetUserFontName(fontKey, fontname, 50);
                                                            result = sAIFont->GetPostScriptFontName(fontKey, psname, 50);
                                                            result = sAIFont->GetFontStyleName(fontKey, stylename, 50);
                                                            result = sAIFont->GetFontFamilyUIName(fontKey, familyname, 50);
}
 
For some fonts(not all the fonts) , Style name is comming as empty string, however for other fonts its working. Not sure why its working for some fonts and not for others. Other font properties are coming fine for all fonts.When its failing, result is not  kNoErr, but i dont know that how to get the exact error?