Excelsior Delivery supports WiX version 3.5 and above. You need to download and install wix35.msi and ProjectAggregator2.msi.
The Windows Installer XML (WiX) is a toolset that builds Windows installation packages from XML source code. WiX is an open source project, originally developed by Microsoft and maintained by Rob Mensching.
You can download the latest binary and source code releases.
The toolset is written in C# and requires the .NET Framework 2.0 and its Service Pack 1 to run. However, this only applies to the toolset itself. The installation packages you create with the toolset do not require any extra framework or software to be installed on the target computer.
Please see http://wix.sourceforge.net/ for more information about the WiX toolset.