Use menu_get_object in block_view instead of args

/**                                                                                
 * Implements hook_block_view().                                                   
 */                                                                                
function prev_next_block_view($delta) {                                            
  $content = '';                                                                   
  $block = array();                                                                
  $next_display = variable_get('prev_next_display_next' . $delta, PREV_NEXT_DISPLAY_DEFAULT);
  $next_text = variable_get('prev_next_display_text_next' . $delta, PREV_NEXT_DISPLAY_TEXT_NEXT_DEFAULT);
  $prev_display = variable_get('prev_next_display_prev' . $delta, PREV_NEXT_DISPLAY_DEFAULT);
  $prev_text = variable_get('prev_next_display_text_prev' . $delta, PREV_NEXT_DISPLAY_TEXT_PREV_DEFAULT);
                                                                                   
  if (arg(0) == 'node' && is_numeric(arg(1)) && !arg(2) ) {                        
    $node = node_load(arg(1));                                                     
    $n_nid = prev_next_nid($node->nid, 'next');                                    
    $p_nid = prev_next_nid($node->nid, 'prev');

 $node = menu_get_object();
  if (menu_get_object()) {
    $node = menu_get_object();
    $nid = $node->nid;
    $n_nid = prev_next_nid($nid, 'next');                                    
    $p_nid = prev_next_nid($nid, 'prev');