The installer for the Orchestrator Integration Toolkit R2 checks the registry for the version of WiX while checking for prerequisites, It is expecting to find the exact version of 3.5. WiX has recently been updated to support Visual Studio 2013 and other fixes you can find the details here.
This is the error you will get if you don’t have WiX installed or if you have any other version than version 3.5
Here are the steps to add the missing Key to your registry:
1. Open the registry HKLMSoftwareWow6432NodeMicrosoftWindows Installer XML
2. Create anew Key named “3.5”
3. Create 3 string values (I copied the values from the current version)
a. InstallFolder = C:Program Files (x86)WiX Toolset v3.8
b. InstallRoot = C:Program Files (x86)WiX Toolset v3.8bin
c. ProductVersion = 3.8.1128.0
Now you should be able to complete the installation of the Orchestrator Integration Toolkit.