c# - Why some directories i can't drag and drop on listBox1? -

this path of folder images inside i'm trying drag , drop listbox1:

c:\users\chocolade1972\appdata\local\mws\my weather station\images

but if drag folder in c:\ example c:\images drag fine listbox1.

when drag user...directory see black symbol can't drop in.

private void listbox1_dragdrop(object sender, drageventargs e)         {             if (e.data.getdatapresent(dataformats.filedrop))             {                 string[] files = (string[])e.data.getdata(dataformats.filedrop);                 label6.text = files.length.tostring();                 filescount = files.length-1;                 beginconvertiontoolstripmenuitem.enabled = true;                 (int = 0; < files.length; i++)                 {                     fileinfo fi = new fileinfo(files[i]);                   if (listbox1.items.contains(fi.fullname))                   {                    }                   else                   {                       string directoryname = fi.directoryname;                       string[] filesextension = directory.getfiles(directoryname).select(p => path.getextension(p)).distinct().orderby(p => p).toarray();                       (int d = 0; d < filesextension.length; d++)                       {                           if (fi.extension.tolower() == filesextension[d])                           {                               listbox1.items.add(fi.fullname);                           }                       }                    }                 }                 this.select();             }         } 

and drag on event:

private void listbox1_dragover(object sender, drageventargs e)         {             if (e.data.getdatapresent(dataformats.filedrop))             {                 string[] files = (string[])e.data.getdata(dataformats.filedrop);                  bool bfound = false;                 (int = 0; < files.length; i++)                 {                     fileinfo fi = new fileinfo(files[i]);                     string directoryname = fi.directoryname;                     string[] filesextension = directory.getfiles(directoryname).select(p => path.getextension(p)).distinct().orderby(p => p).toarray();                     (int d = 0; d < filesextension.length; d++)                       {                           if (fi.extension.tolower() == filesextension[d])                         {                             bfound = true;                         }                       }                 }                  if (bfound)                     e.effect = dragdropeffects.copy;                 else                     e.effect = dragdropeffects.none;             }             else                 e.effect = dragdropeffects.none;          }