(DB2 v7.2 FixPak 7 migrating to v8.1 FixPak 0 on AIX5.2)

We have 2-way replication running on 2 databases (i.e. with capture
and apply running on both).

The following command runs successfully:
asnmig8 db <database> on control server using schema backup for
migration
But then I run the following command is run subsequently on the same
database
asnmig8 db <database> on source server using schema backup for
migration
and get the following (undocumented) error:-
======
ASN5012E After control table script, only SOURCE-server backup is
valid.
ASN5000E asnmig8 for migration is abnormally ending at Fri Sep 5
15:02:01 2003.
======

If I attempt to migrate the source server again I get a new error:
======
ASN5014E After migration, migration is complete, and only
SOURCE-server fallback is valid if desired.
ASN5001I A successful migration is complete at Fri Sep 5 16:01:33
2003.
======

(A similar error is reported if, having successfully migrated the
source server, I then attempt to migrate the control server).

Can anyone help?

Thank you very much.