ejabberd doesn't work under high load

Hi everybody, as in the post before I could solve the problem of importing jabberd1.4 users, but it looks like it doesn't work anyway when exposed to the high load of the main server, whereas it worked ok on a secondary port on the same server.

The HTTP admin interface stopped working, I couldn't login and ejabberdctl gave this error message:

root@picard:/var/lib/ejabberd#ejabberdctl registered-users
Can't get list of registered users at node ejabberd@picard: {'EXIT',
                                                                {badarg,
                                                                    [{erlang,
                                                                         port_control,
                                                                         [stringprep_port,
                                                                          1,
                                                                          "jabber.linux.it"]},
                                                                     {stringprep,
                                                                         control,
                                                                         2},
                                                                     {jlib,
                                                                         nameprep,
                                                                         1},
                                                                     {ejabberd_auth,
                                                                         auth_module,
                                                                         1},
                                                                     {ejabberd_auth,
                                                                         dirty_get_registered_users,
                                                                         0},
                                                                     {rpc,
                                                                         '-handle_call/3-fun-0-',
                                                                         5}]}}

I used the options -env ERL_MAX_PORTS 5000 +P 250000 -env ERL_MAX_ETS_TABLES 20000 as written in http://www.ejabberd.im/tuning.

I would hate to try and switch to another jabber server yet, but it looks like I can't make ejabberd work and jabberd1.4 can't handle the load on my machine. Any ideas?

Thanks
Matteo