Oracle Update-question

I am updating a table with a value used in another table. Now my Oracle skills are slowly coming back up to speed, but would appreciate any help on this:
Baan Application:

UPDATE ttcibd001100 a
SET a.t$seab=(SELECT b.t$otbp from ttdipu001100 b
where b.t$item=a.t$item and b.t$otbp is not null
and substr(a.t$item,10,6)>'53-A00000.0000'
and substr(a.t$item,10,6)<'53-A15006.6250'
)
/

Following a similar example in oracle sql book page 292-293:
example:
BEGIN
UPDATE emp e
SET sal=(SELECT sal * 0.90
from emp m
where e.mg =m.empno)
where mg is not null
END;

The code gets hung up on the b.t$otbp.
Objective:
Set value of ttcibd001100.seab = ttdipu001100.otbp based on an range of items:
and substr(a.t$item,10,6)>'53-A00000.0000'
and substr(a.t$item,10,6)<'53-A15006.6250'

Gets error:
cannot update ("BAAN"."TTCIBD001100"."T$SEAB") to NULL

Porbably the t$seab column has a not null constraint and the subselect returns an empty set.

Thanks for your replys: I did however, put in the following condition so that if NULLS where hit, they would not get through:

UPDATE ttcibd001100 a
SET a.t$seab=ttdipu001100.otbp
WHERE EXISTS(Select b.t$item from ttdipu001100 b
WHere b.t$item=a.t$item
and b.t$otbp is not null
and substr(a.t$item,10,14)>='53-A00000.0000'
and substr(a.t$item,10,14)<='53-A016088.6250'
)
/

However, it still errors indiciating that the
a.t$seab=ttdipu001100.otbp 'ttdipu001100.0tbp is a value the SQLPLUS does not understand.

I changed the script to :
UPDATE ttcibd001100 a SET a.t$seab='SUP000102'
WHERE EXISTS(select b.t$item,b.t$otbp from ttdipu001100 b
WHERE b.t$item=a.t$item
/* Update group 1*/
AND substr(b.t$item,10,14)>='53-A00000.0000'
AND substr(b.t$item,10,14)<='53-A01608.6250'
)
/

And things get done correctly. But this is a straightforward hard update rather than a dynamic update. Anyone have any other ideas?
Thanks to all!
Jeff Laatsch

I noticed that your parameters in the sub-query changed a little from your first post to your last... did you try

UPDATE ttcibd001100 a
SET a.t$seab=(SELECT b.t$otbp from ttdipu001100 b
where b.t$item=a.t$item and b.t$otbp is not null
and substr(b.t$item,10,6)>'53-A00000.0000'
and substr(b.t$item,10,6)<'53-A15006.6250'
)
/

substituting a.t$item with b.t$item?

Oracle don't understand this value, use to_number or to_char conversion. Instead where a > c and a < d use where a between c and d.

declare
cursor c is select t$otbp,t$item from ttdipu001100
where t$otbp is not null and substr(t$item,10,14) between '53-A00000.0000' and '53-A016088.6250' ;
begin
for v in c loop
UPDATE ttcibd001100 SET t$seab=v.t$otbp where t$item=v.t$item;
--- eventualy insert here a commit after every x (depends on your log files) updates
end loop;
commit;
end;