call_user_func_array() in menu.inc breaks image gallery

Hi,

my watchdog log is cluttered with error messages like this:

call_user_func_array() [<a href='function.call-user-func-array'>function.call-user-func-array</a>]: First argument is expected to be a valid callback, 'image_gallery_page' was given in /var/www/drupal/includes/menu.inc in line 348.

These errors are caused by accessing an image gallery as provided by image module; those vews-based gallery are not being displayd, instead I'm getting a blank screen (WSOD?). ./admin/reports/status indicates no problems, and update.php has neither pending updates nor errors.

With the help of one of the image.module maintainers (Joachim) I was able to exclude a malfunction inside image.module (cf. #571504: Galleries not working anymore); since the error points somehow to Drupal core's menu router, I hope this is the right place to post this issue.

What we tried was to put an print_r(debug_backtrace()); before line 348 (which is return call_user_func_array($router_item['page_callback'], $router_item['page_arguments']);) mentioned in the watchdog error message. That gave me a blank page with the following textual output:

Array ( [0] => Array ( [file] => /var/www/drupal/index.php [line] => 18 [function] => menu_execute_active_handler [args] => Array ( ) ) )

Next we tried to put an print_r($router_item); before line 348. That gave me the following output (again on a blank page):

Array ( [path] => image/tid/% [load_functions] => Array ( [2] => ) [to_arg_functions] => [access_callback] => user_access [access_arguments] => a:1:{i:0;s:14:"access content";} [page_callback] => image_gallery_page [page_arguments] => Array ( [0] => tid [1] => 1917 ) [fit] => 6 [number_parts] => 3 [tab_parent] => [tab_root] => image/tid/% [title] => Image galleries [title_callback] => t [title_arguments] => [type] => 4 [block_callback] => [description] => [position] => [weight] => 0 [file] => [href] => image/tid/1917 [options] => Array ( ) [access] => 1 [localized_options] => Array ( ) [map] => Array ( [0] => image [1] => tid [2] => 1917 ) )

As Joachim explained, there is an empty [file] => statement that shouldn't be empty. The expected output should be:

/**
* Implementation of hook_menu().
*/
function image_gallery_menu() {
  $items = array();

  $items['image'] = array(
    'title' => 'Image galleries',
    'access arguments' => array('access content'),
    'type' => MENU_SUGGESTED_ITEM,
    'page callback' => 'image_gallery_page',
    'file' => 'image_gallery.pages.inc', <------- this is the line your system seems to not be picking up!
  );

Sorry, I can't provide steps to reproduce this error. However, I can reproduce it on my site, and of course I'm willing to help debugging this issue if someone provides instructions I can follow (but beware, I have no coding experience).

Thanks & greetings, -asb