Sorry about previous misinformation, I was lookng at PowerStore 3, not PowerStore4.
From what I can work out, user_update.php is an extraneous file (which would return an error in anybody's version of PowerStore 4) but is not actually used or referenced in this solution.
This should not affect the working of the Store (as far as I can work out) as the store refers to users_update.php.
I have visited various PowerStore4 sites and added 'admin/user_update.php' after each store address, and each one throws an error:
Fatal error: require_once() [function.require]: Failed opening required '../WA_Globals/WA_Globals.php' (include_path='.:/usr/local/php5/lib/php') in /home/content/l/i/s/lisaellen/html/admin/user_update.php on line 1
Maybe a WA tech will throw a little light on its inclusion on Monday.