An unknown error has ocurred - One solution

Today I was setting up a fresh virtual machine with MOSS 2007 and I met the dreaded "An unknown error has ocurred" message after the SharePoint Configuration Wizard finished.

I traced it in the Event Viewer and it was a repetitive error such as this one:

The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID
{61738644-F196-11D0-9953-00C04FD919C1}
to the user NT AUTHORITYNETWORK SERVICE SID (S-1-5-20). This security permission can be modified using the Component Services administrative tool.

I looked up in the Registry and found out that the CLSID in the message identified one "IIS WAMREG admin service". Then, I opened the Component Services, DCOM Config and under the properties of WAMREG service component I allowed NETWORK SERVICE account local launch and local activation permissions (on the Security tab).

The MOSS 2007 fresh welcome was just one IISRESET away!