Re;
Problem found. It's only because I've forgot to update the onAfterAddDomainAlias listener according the db update...
You can solve this problem by replacing the line 235 and 236 from the /var/www/imscp/gui/plugins/OpenDKIM/OpenDKIM.php file by:
Anyway, I'll release the version 0.0.3 now.
Thank for your report.