> Guido,
> are you trying to select fields from these two tables where the same
> fieldname exists?
> are you using aliases?

That's a good question :-) The problem is, that the Replication-Manager from
the product IBReplicator produces this error and I don't know, what it is
internally doing. BTW, only with FB, with IB all works fine.
I have seen in the Closed Bugs of FB the following:
Unions that work with earlier versions and use same tables usually get this
errors for example (employee.gdb):
SELECT J.PROJ_ID,J.PROJ_NAME,1
FROM PROJECT J
UNION
SELECT J.PROJ_ID,J.PROJ_NAME,2
FROM PROJECT J

Dynamic SQL Error
SQL error code = -204
Ambiguous field name between table/view PROJECT and
table/view PROJECT PROJ_ID.
In fact, there is not ambiguity here because each select is independent and
has his aliases or tables, traditionally because this ORDER BY clause in UNION
must use numbers instead of field names.

But there is also written, that this bug is fixed in v1.0


Guido