Exchange 2003 -2010 cross forest (NDR 5.4.6)

Hi.

Have: Exchange 2003+2010 in source forest. Exchange 2010 in target forest.

Successful migrate mailbox to target forest (in source forest this mailbox convert to mailuser).
When try send e-mail to this mailbox (it`s in target forest) from Exchange 2003 mailbox get this:
A configuration error in the e-mail system caused the message to bounce between two servers or to be forwarded between two recipients.

If send from Exchange 2010 (source/target) - all mail ok.
If delete this mailuser (in source forest) - all set to ok.

x500?


Please, help.
Thanks.