Although i have found the fix of this problem, but i thought of sharing with others.
Problem is if you mention $rows & theme_table like following:
$row = array('data' => drupal_render($form[$key]['alt_name']), 'class' => 'alt-ing-name-td'); $output = theme_table(array('header' => $header, 'rows' => $rows,'attributes' => array('id' => 'recipe-id')));
then you will get following error:
Fatal error:  operator not supported for strings in theme.inc