Database Software

I recently acticated replication between two Oracle instances.
(one being the master definition site and the other one being
a second master site).

Everything was going well until two weeks ago, when i realized
that some datas were different between the two Oracle instances.
I tried to figure out why and found that some deferred transation
failed to propagate due to a "ORA-01403: no data found" error.
Not all transaction fail, only a few.

All the errors are stored in the DEFERROR table of the second
master site, the DEFERROR table is empty in the master definition
site.

For every error, the source is the master definition site and the
destination is the second master site, which is OK because the
second master site is supposed to be "read-only". But why are the
errors stored in the DEFERROR table of the second master site
(and not in the master definition site (the source)).

Most errors occur on UPDATE statements but a few of them occur
on DELETE statements. Given the fact that the record actually is
in the second master site, how is it possible to get a
"ORA-01403: no data found" error on a delete statement ???????

I can't figure out what data cannot be found,

Thanks for your help,

Didier.