When deleting a domain from Helm, it fails and I get the following error in the logs:
2004-03-19 09:51:18 CDomain.DeleteDomainEx Object doesn't support this property or method
2004-03-19 09:51:18 CEmail.RemoveEmailAccount Object doesn't support this property or method
This suggests that the DLL for the mail interface is not installed correctly in COM+. To rectify this, open the Helm Configuration Tool, and click the System Identity tab. Re-enter your HELM_ADMIN password twice and click the check box for Rebuild Helm COM+ Applications (Advanced).
This will give you a prompt to continue, and another prompt when it has completed. Once completed, try and delete the domain in Helm again. It should now work - if not, refer to your support provider.