SSL_CTX_use_certificate_file failed: error:02001002:system library:fopen:No such file or directory

ejabberd: 2.0.1 lenny package
erlang: 5.6.3
Debian Lenny

Very strange behavior:
- when I try to connect to the jabber server, my Gajim client open a popup to tell me "This connection is not secured. Your are ready to connect to an unsecured connection, This means all your conversations will be unencrypted, you should not use it[...]" (approx. translation) etc.
- installation is a really basic one (configuration file below)
- I tried a lot of things without any success.

Any help would be welcome.
Best regards
Phil

%%%%--------------%<------------ /etc/ejabberd/ejabberd.cfg extract
{loglevel, 4}.
{watchdog_admins, [""]}.
{listen,
[
{5222, ejabberd_c2s, [
{access, c2s},
{shaper, c2s_shaper},
{max_stanza_size, 65536},
starttls, {certfile, "/etc/ejabberd/ejabberd.pem"}
]},
{5269, ejabberd_s2s_in, [
{shaper, s2s_shaper},
{max_stanza_size, 131072}
]},
{5280, ejabberd_http, [
http_poll,
web_admin
]}
]}.
{s2s_use_starttls, true}.
{s2s_certfile, "/etc/ejabberd/ejabberd.pem"}.
{s2s_default_policy, allow}.
{auth_method, internal}.
{shaper, normal, {maxrate, 10000}}.
{shaper, fast, {maxrate, 500000}}.
{acl, local, {user_regexp, ""}}.
{access, max_user_sessions, [{15, all}]}.
{access, local, [{allow, local}]}.
{access, c2s, [{deny, blocked},
{allow, all}]}.
{access, c2s_shaper, [{none, admin},
{normal, all}]}.
{access, s2s_shaper, [{fast, all}]}.
{access, announce, [{allow, admin}]}.
{access, configure, [{allow, admin}]}.
{access, muc_admin, [{allow, admin}]}.
{access, muc, [{allow, all}]}.
{access, register, [{deny, all}]}.
{access, pubsub_createnode, [{allow, all}]}.
{language, "en"}.
{modules,
[
{mod_adhoc, []},
{mod_announce, [{access, announce}]}, % requires mod_adhoc
{mod_caps, []},
{mod_configure,[]}, % requires mod_adhoc
{mod_ctlextra, []},
{mod_disco, []},
{mod_irc, []},
{mod_last, []},
{mod_muc, [
{access, muc},
{access_create, muc},
{access_persistent, muc},
{access_admin, muc_admin},
{max_users, 500}
]},
{mod_offline, []},
{mod_privacy, []},
{mod_private, []},
{mod_proxy65, [
{access, local},
{shaper, c2s_shaper}
]},
{mod_pubsub, [ % requires mod_caps
{access_createnode, pubsub_createnode},
{plugins, ["default", "pep"]}
]},
{mod_register, [
{welcome_message, none},
{access, register}
]},
{mod_roster, []},
{mod_stats, []},
{mod_time, []},
{mod_vcard, []},
{mod_version, []}
]}.

%%%%--------------%<------------ ejabberd.log extract

=INFO REPORT==== 2012-05-18 17:47:45 ===
I(<0.263.0>:ejabberd_listener:112) : (#Port<0.417>) Accepted connection {{193,227,130,98},24669} -> {{10,10,30,9},5222}

=ERROR REPORT==== 2012-05-18 17:47:45 ===
** State machine <0.349.0> terminating
** Last event in was {xmlstreamelement,
{xmlelement,"starttls",
[{"xmlns","urn:ietf:params:xml:ns:xmpp-tls"}],
[]}}
** When State == wait_for_feature_request
** Data == {state,{socket_state,gen_tcp,#Port<0.417>,<0.348.0>},
ejabberd_socket,#Ref<0.0.0.8830>,"3379169216",
{sasl_state,"jabber","teicee.fr",[],
#Fun,
#Fun,undefined,
undefined},
c2s,c2s_shaper,false,true,false,false,
[{certfile,"/etc/ejabberd/ejabberd.pem"}],
false,undefined,[],"teicee.fr",[],undefined,
{0,nil},
{0,nil},
{0,nil},
{0,nil},
{dict,0,16,16,8,80,48,
{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],
[]},
{{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],
[]}}},
undefined,undefined,undefined,false,
{userlist,none,[]},
unknown,unknown,
{{193,227,130,98},24669},
"fr"}
** Reason for termination =
** {{badmatch,{error,"SSL_CTX_use_certificate_file failed: error:02001002:system library:fopen:No such file or directory"}},
[{ejabberd_socket,starttls,3},
{ejabberd_c2s,wait_for_feature_request,2},
{p1_fsm,handle_msg,10},
{proc_lib,init_p,5}]}

=INFO REPORT==== 2012-05-18 17:47:45 ===
I(<0.263.0>:ejabberd_listener:112) : (#Port<0.428>) Accepted connection {{193,227,130,98},7703} -> {{10,10,30,9},5222}

=INFO REPORT==== 2012-05-18 17:47:49 ===
I(<0.263.0>:ejabberd_listener:112) : (#Port<0.430>) Accepted connection {{64,134,225,52},56478} -> {{10,10,30,9},5222}

%%%%--------------%<------------ sasl.log extract

=CRASH REPORT==== 18-May-2012::17:47:45 ===
crasher:
pid: <0.349.0>
registered_name: []
exception exit: {{badmatch,{error,"SSL_CTX_use_certificate_file failed: error:02001002:system library:fopen:No such file or directory"}},
[{ejabberd_socket,starttls,3},
{ejabberd_c2s,wait_for_feature_request,2},
{p1_fsm,handle_msg,10},
{proc_lib,init_p,5}]}
in function p1_fsm:terminate/7
initial call: gen:init_it(p1_fsm,<0.254.0>,<0.254.0>,ejabberd_c2s,
[{ejabberd_socket,
{socket_state,gen_tcp,#Port<0.417>,
<0.348.0>}},
[{access,c2s},
{shaper,c2s_shaper},
{max_stanza_size,65536},
starttls,
{certfile,"/etc/ejabberd/ejabberd.pem"}]],
[{max_queue,1000}])
ancestors: [ejabberd_c2s_sup,ejabberd_sup,<0.37.0>]
messages: []
links: [<0.254.0>,#Port<0.426>]
dictionary: [{'$internal_queue_len',0}]
trap_exit: false
status: running
heap_size: 1597
stack_size: 23
reductions: 1812
neighbours:

=SUPERVISOR REPORT==== 18-May-2012::17:47:45 ===
Supervisor: {local,ejabberd_c2s_sup}
Context: child_terminated
Reason: {{badmatch,{error,"SSL_CTX_use_certificate_file failed: error:02001002:system library:fopen:No such file or directory"}},
[{ejabberd_socket,starttls,3},
{ejabberd_c2s,wait_for_feature_request,2},
{p1_fsm,handle_msg,10},
{proc_lib,init_p,5}]}
Offender: [{pid,<0.349.0>},
{name,undefined},
{mfa,
{ejabberd_c2s,start_link,
[{ejabberd_socket,
{socket_state,gen_tcp,#Port<0.417>,<0.348.0>}},
[{access,c2s},
{shaper,c2s_shaper},
{max_stanza_size,65536},
starttls,
{certfile,"/etc/ejabberd/ejabberd.pem"}]]}},
{restart_type,temporary},
{shutdown,brutal_kill},
{child_type,worker}]