Sync2DB Web Services could not be installed

SYMPTOMS:
When you try to install the Sync2DB Web Services, you would receive the following error message:
“The installer was interrupted before Sync2DBWeb Setup could be installed. You need to restart the installer to try again. Click Close to exit.”

You reboot and get the same message.

CAUSE:
It is a known and old IIS/.NET issue.
You have installed the MS IIS (Internet Information Services) after MS .NET Framework installation.

RESOLUTION:
The best practice is to install the IIS before the .NET Framework.
When you install the .NET Framework on a system that has IIS already installed, IIS is configured automatically.

But if you decide to install IIS after installing the .NET Framework, after the IIS installation you will need to use a utility shipped with the .NET Framework: aspnet_regiis.exe. It is located under %WindowsDir%\Microsoft.NET\Framework\vx.y.zzzz\ and must be called with the -i parameter: aspnet_regiis.exe -i

Source: http://www.devx.com/vb2themax/Tip/18849 (thanks to Marco Bellinaso).