Error during DLP Maintenance Pack installation: "The feature you are trying to use is on a network resource that is unavailable"

Products

• Data Loss Prevention
• Data Loss Prevention Core Package
• Data Loss Prevention Enforce

Issue/Introduction

During an attempt to install a Maintenance Pack from an .msp file, for any DLP version, either on Enforce or on a detection server, a popup is displayed with the following error:

The feature you are trying to use is on a network resource that is unavailable. Click OK to try again, or enter an alternate path to a folder containing the installation package 'EnforceServer.msi' is the box below.

The error will reference EnforceServer.msi when seen on Enforce, or DetectionServer.msi when seen on a detection server. 

Cause

This issue is directly related to how Microsoft Installer (msiexec) performs installation of DLP software when the base version of a specific build is installed, either for the purpose of a fresh install or an upgrade. During an installation of a base DLP version from a source .msi file, msiexec makes a copy of that file, gives it a random filename, and places that copy under the path C:\Windows\Installer. This location is named Windows Installer Cache. 

An entry will also be added to the Registry under the following key:

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products\<ProductID>\InstallProperties\LocalPackage

The value of that key will be the path to that temp copy of the original .msi, placed under C:\Windows\Installer.

Later during an attempt to install an MP for that specific DLP version, msiexec will look for that local package in the same location. If however the local package was removed i.e. as part of an OS cleanup or maintenance, msiexec will then try to look for the original .msi file in the same location from which the .msp MP installer is ran. If the file is not found there, a popup will be displayed showing the error. 

Resolution

To fix the error, follow the below process:

1. Copy the original .msi file for the base build for either Enforce or detection server back to the machine where you are installing the MP. It is important that it has to be the same base build as what is the MP which you are trying to install - for example if you try to install the 16.1 MP1, you have to put the 16.1 installer MSI on the server. 
2. Place the file in the same location where the .msp installer for the MP is already placed
3. Re-run the MP installation.
4. If the popup appears again:
   1. Use the Browse button to point the popup to the location of where you placed the original .msi.
   2. Msiexec will then again:
      1. Create a copy of the .msi under C:\Windows\Installer
      2. Update the Registry entry
      3. Proceed with installing the Maintenance Pack