not uploaded successfully dropzone images thumbnail

I am working with dropzone image uploder in laravel. but when I drag images to dropzone box image thumbnail displaying a cross and error. how can fix this problem? my form,

     <div class="row">
        <div class="col-sm-10 offset-sm-1">
            <h2 class="page-heading">Upload your Images <span id="counter"></span></h2>

            <div class="clsbox-1" runat="server"  >
        <div class="dropzone" id="my-dropzone">
        <div class="fallback">
    <input name="file" type="file" multiple />
  </div>

how can solve this problem?

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