As we were deploying a WCF service via web setup projects on Windows Server 2008 with IIS 7.0, the setup failed with the installer saying
"The installer was interrupted before [my app] could be installed. You need to restart the installer to try again."
Of course after restarting the installer, the exact same error occurred again. :-)
It seems that the MSI package is using the Metabase feature of IIS6. As this is not installed by default on an IIS7 machine, you get an error. Installing the IIS 6 Metabase Compatibility Component solves the issue. (it's situated under Role Services in the Server Manager)