// setting property to determine the rendered images fields
$form['best_responsive_settings']['imagesCount'] = array(
      '#markup' => t('Enter the total number of images in the slideshow'),
      '#type' => 'select',
      '#options' => associate_array_vals(explode(',',  theme_get_setting('imagesCountOptions'))),
      '#selected' => theme_get_setting('imagesCount'),
      '#default_value' => theme_get_setting('imagesCount'),

  );

  $lang_list = language_list();
// rendering upload image form with caption textfield for every language supported by the website

  for ($i = 0; $i < theme_get_setting('imagesCount'); $i++){
      $form['best_responsive_settings']['slideshowImages'.$i] = array(
        '#type' => 'managed_file',
        '#title' => t('Image').' #'.($i+1),
         '#required' => false,
        '#upload_location' => file_default_scheme() . '://slides',
    '#default_value' => theme_get_setting('slideshowImages'.$i,'best_responsive'),
    '#upload_validators' => array(
      'file_validate_extensions' => array('gif png jpg jpeg'),
      'file_validate_image_resolution' => array('960x400','430x400')        ),

      );
      foreach ($lang_list as $lang){
      $form['best_responsive_settings']['slideshowCaption'.$lang->language.$i] = array(
    '#type' => 'textfield',
    '#title' => t('Caption').' #'.($i+1).' -- '.$lang->name,
    '#required' => false,
    '#default_value' => theme_get_setting('slideshowCaption'.$lang->language.$i, 'best_responsive'),
  );
      }
  }

<?php if (theme_get_setting('slideshow_display','best_responsive')): ?>

    <div id="home-slider">
      <div class="flexslider-container">
        <div id="single-post-slider" class="flexslider">
          <ul class="slides">
            <?php for ($i = 0; $i < theme_get_setting('imagesCount'); $i++): ?>
              <?php  if (theme_get_setting('slideshowImages'.$i) != ''): ?>
 //the following line causes a problem after some time
            <li class="slide"><img src="<?php echo file_create_url(file_load(theme_get_setting('slideshowImages'.$i))->uri);?>" alt="Slide"/><?php if (theme_get_setting('slideshowCaption'.$language->language.$i)): ?><span class="flex-caption"><?php echo theme_get_setting('slideshowCaption'.$language->language.$i) ;?></span><?php endif;?></li>

              <?php endif; ?>
            <?php endfor; ?>
          </ul><!-- /slides -->
        </div><!-- /flexslider -->
      </div>
    </div>
    <?php endif; ?>
    <?php endif; ?>

Notice: Trying to get property of non-object in include() (line 159 of C:xampp-2htdocs4testdrupal-7.28sitesallthemesbest_responsivetemplatespage.tpl.php).