Can you help with a CLOB problem?

Started getting an error reported:

ORA-06502: PL/SQL: numeric or value error
ORA-06512: at "SYS.DBMS_LOB", line 789
ORA-06512: at "WD.WD_FAB", line 11065
ORA-06512: at "WD.WD_FAB", line 10288

Line 10288 is:
10286 l_fab_form.view_form_score_intro := 10287 replace (l_fab_form.view_form_score_intro,'[score]',p_score); 10288 append(l_fab_form.view_form_score_intro, 10289 l_clob);

Line 11065 is in the procedure (in same package):

..... procedure append
..... (p_in in varchar2,
..... p_out in out clob)
..... is
.....
..... begin
.....

11655 dbms_lob.writeappend( p_out, LENGTH( p_in ), p_in );
.....
..... end append;

l_fab_form is defined as wd_fab_forms%rowtype;

And the view_form_score_intro column is a varchar2(4000).

What is puzzling is that the "append" procedure is used repeatedly in the same execution of the procedure using similar columns e.g.

we start off with:

• Initialize CLOB dbms_lob.CreateTemporary( l_clob, TRUE );

Then e.g.

• open an outer table append(htf.tableopen(cattributes=>'border="0"') ||chr(10) ||htf.tablerowopen ||chr(10) ||'<TD>', l_clob);

Then e.g.

    append(l_fab_form.view_form_intro,

           l_clob);

which works fine (and view_form_intro is also a varchar2(4000)).

That's when we come to the call to "append" which is failing. There are also several calls to "append" after the one which fails, all of which work absolutely fine (when I comment out the 'problem' line).

I am a bit stumped, could anyone shed any light on why this particular call to "append" might cause an error?

Thanks.

-- 
jeremy

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   ENVIRONMENT:                                             
   Oracle 9iR2 / Oracle HTTP Server / mod_plsql / Solaris 8 
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