[wp-hackers] WP admin users.php for more than 40k users

[Malaiac]

users.php did not work for a few days.
The script stops on "get_users_of_blog()" (in wp-includes/user.php)
called from wp-admin/users.php on line 255

We have more than 40 000 users on this install...
Server is a dedicated Dell, load average is ok (between 0.5 and 2,
while it had sustained before load of 30-60 for days)

Is there natural limits to WP specs concerning user database ?

Malaiac