To resolve this issue please add the following parameter to the Default INI.
Determines whether the Data Migration Wizard will migrate the identities of mail-in database owners when it migrates mail-in DBs. The Directory Export Wizard captures these owner identities to MNE's SQL database in any case, but the migration of the identities to Exchange is an option that is enabled or disabled by this boolean program parameter.
By default (MigrateMailInDBOwner=1), the wizard will migrate the identities of mail-in DB owners.
To disable this feature, set MigrateMailInDBOwner=0