Error attempting to unlock unowned resource

I get the following error when running a procedure tree
Process ID 55 attempting to unlock unowned resource PAG:8:1:4889
And in the server log : Error: 1203, Severity: 20, State: 1
This error is referenced more than one before SP3, but newer since.
I saw all KB to see if some query type are similar to mine, without success.
The following query is executed inside a procedure at the 4th level,
without transaction.
I couln't simply reproduce the problem without calling the first, who's
calling the second, ...
Standalone calling the procedure works like a charm.
Thanks in advance for your help.
Involving query :
DECLARE @.i_tou_niveau INT
SELECT @.i_tou_niveau = 6
UPDATE liasse_rq SET
lia_trav1 = @.i_tou_niveau,
lia_trav3 = o.p_ocd_regr
FROM liasse_rq l, ocd_regr o
WHERE l.lia_c_type_vdd = "PTT"
AND l.lia_niveau BETWEEN 1 AND 2
AND l.p_tou_id = 0
AND o.ocd_niveau = @.i_tou_niveau
AND o.ocd_min <= l.lia_ocd
AND o.ocd_max >= l.lia_ocd
Tables:
if exists (select * from dbo.sysobjects where id =
object_id(N'[dbo].[ocd_regr]') and OBJECTPROPERTY(id,
N'IsUserTable') = 1)
drop table [dbo].[ocd_regr]
GO
if exists (select * from dbo.sysobjects where id =
object_id(N'[dbo].[liasse_rq]') and OBJECTPROPERTY(id,
N'IsUserTable') = 1)
drop table [dbo].[liasse_rq]
GO
if exists (select * from dbo.systypes where name =
N't_code')
exec sp_droptype N't_code'
GO
if exists (select * from dbo.systypes where name =
N't_npa')
exec sp_droptype N't_npa'
GO
setuser
GO
EXEC sp_addtype N't_code', N'varchar (4)', N'null'
GO
setuser
GO
setuser
GO
EXEC sp_addtype N't_npa', N'varchar (10)', N'null'
GO
setuser
GO
CREATE TABLE [dbo].[ocd_regr] (
[p_ocd_regr] [varchar] (7) COLLATE French_CI_AI
NOT NULL ,
[ocd_nom] [varchar] (20) COLLATE French_CI_AI NOT
NULL ,
[ocd_min] [int] NOT NULL ,
[ocd_max] [int] NOT NULL ,
[ocd_niveau] [tinyint] NOT NULL ,
[timestamp] [timestamp] NULL
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[liasse_rq] (
[p_lia_id] [int] IDENTITY (1, 1) NOT NULL ,
[lia_c_type_vdd] [t_code] NOT NULL ,
[p_tou_id] [int] NOT NULL ,
[p_vdd_id] [int] NOT NULL ,
[p_edi_id] [int] NOT NULL ,
[lia_nom] [varchar] (28) COLLATE French_CI_AI NOT
NULL ,
[lia_mode_encartage] [tinyint] NOT NULL ,
[lia_qte] [int] NOT NULL ,
[lia_pos] [int] NOT NULL ,
[lia_niveau] [tinyint] NOT NULL ,
[p_pay_id] [int] NULL ,
[lia_npa] [t_npa] NULL ,
[lia_b_ptt2plis] [tinyint] NOT NULL ,
[lia_b_mono] [tinyint] NOT NULL ,
[lia_ocd] [int] NULL ,
[lia_circonscription] [int] NULL ,
[p_amb_id] [int] NULL ,
[p_etr_id] [int] NULL ,
[lia_c_achemin_pe] [t_code] NULL ,
[lia_npa_n] [int] NULL ,
[p_ocd_regr] [varchar] (7) COLLATE French_CI_AI
NULL ,
[lia_trav1] [int] NULL ,
[lia_trav2] [int] NULL ,
[lia_trav3] [varchar] (10) COLLATE French_CI_AI
NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[ocd_regr] WITH NOCHECK ADD
CONSTRAINT [ocd_regr_pk] PRIMARY KEY CLUSTERED
(
[p_ocd_regr]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[liasse_rq] WITH NOCHECK ADD
CONSTRAINT [liasse_rq_pk] PRIMARY KEY CLUSTERED
(
[p_lia_id]
) ON [PRIMARY]
GO
CREATE UNIQUE INDEX [ocd_regr_u1] ON [dbo].[ocd_regr]
([ocd_niveau], [ocd_min], [ocd_max], [p_ocd_regr]) ON
[PRIMARY]
GO
CREATE INDEX [liasse_rq_i1] ON [dbo].[liasse_rq]
([p_tou_id]) ON [PRIMARY]
GO
Server Info:
Microsoft SQL Server 2000 - 8.00.760 (Intel X86)
Dec 17 2002 14:22:05
Copyright (c) 1988-2003 Microsoft Corporation
Developer Edition on Windows NT 5.2 (Build 3790: )
Did you able to fix this problem? Plese let me know...