This seems to actually be a problem in Drupal itself. In /modules/file/file.field.inc the function file_field_widget_form has a line like this near the bottom (just before the return statement):

$elements['#file_upload_description'] = theme('file_upload_help', array('description' => '', 'upload_validators' => $elements[0]['#upload_validators'])); 

The issue is a small if condition a few lines back which looks like this:

if (($field['cardinality'] == FIELD_CARDINALITY_UNLIMITED || $delta < $field['cardinality']) && empty($form_state['programmed'])) {     $elements[$delta] = $element;     ...     some more stuff } 

Since I am submitting my form programatically with drupal_form_submit, it adds in $form_state[‘programmed’], thus the if condition fails, $elements[0] does not exist and I get the error

Notice: Undefined offset: 0 in file_field_widget_form() 

My form is submitted by a custom routine (in a custom module) that looks a bit like this:

foreach ($field_data as $k => $detail) {     $field_key = _get_field_keys('field_' . $k);     $field_key = $field_key[0];      $node -> {'field_' . $k}[$node -> language][0][$field_key] = $detail;     $form_state['values']['field_' . $k] = $detail;    }  drupal_form_submit("{$node->type}_node_form", $form_state, $node); 

The form state before I call drupal_form_submit looks like this:

Array (     [values] => Array         (             [title] => some title             [name] => admin             [op] => Save             [field_person] => 88             [field_lead_type] => 1             [field_lead_details] => some stuff     ) 

)

What is the fix? I’d rather not mess with core modules. Is there something I can do to my own code to resolve the problem?