I got the same behavior when I did an upgrade to wp-openid 3.1.2.
The code at line 26 of openid.php is
if (!is_readable('/dev/urandom')) define( 'Auth_OpenID_RAND_SOURCE', null );
which just seems to be checking that /dev/urandom is readable, and if not it sets Auth_OpenID_RAND_SOURCE to null. The upgrade succeeds, but admin pages give that error message.
