First argument to array_keys() should be an array in includes/menu.inc on line 1199.

I'm getting the following error over and over:

warning: First argument to array_keys() should be an array in /home/projects/wapnews2/wapnews2/webroot/includes/menu.inc on line 1199.

This is a new drupal installation, on debian woody. php4.1

Any ideas what caused it to be passing something that's not an array in line 1199:
// Menu items not in the DB get temporary negative IDs.
$temp_mid = min(array_keys($_menu['items'])) - 1;

if is safe to add if (is_array($menu['items'])) just to get the site going?