Upgrade XCOM for Windows 11.6 to 12.0 hangs installing Uninstaller.exe (38%)

Products

• XCOM Data Transport
• XCOM Data Transport - Windows

Issue/Introduction

Upgrading XCOM for Windows 11.6 SP02 to 12.0 using the 12.0 installer XCOM_12_0_23053.exe ,
Using LAX_VM to start installer because just running XCOM_12_0_23053.exe did not do anything i.e. seemed to exit immediately per this article: XCOM for Windows 12.0 installer exits immediately (3004)

Have chosen LAX_VM to be the JRE installed under XCOM 11.6 SP02 so using this command to start the 12.0 installer:
XCOM_12_0_23053.exe LAX_VM "C:\Program Files\CA\XCOM\JRE\1.8.0_144\bin\java.exe"

The installer starts and when prompted for the java.exe location, the same "C:\Program Files\CA\XCOM\JRE\1.8.0_144\bin\java.exe" was selected.
However the installer stops/hangs at 38% showing "Installing... Uninstaller.exe"

Cause

Support tested the same scenario.
They recreated the problem with CTRL key pressed at installer start which opens debug console and it shows a Java error:
*****
Execute Custom Code
    class com.ca.xcom.installer.common.MigrateIni.install() Unexpected Fatal Error:
java.lang.InternalError: java.io.FileNotFoundException: \C:\Program Files\CA\XCOM\JRE\1.8.0_144\lib\ext\dnsns.jar
        at sun.misc.URLClassPath$JarLoader.getResource(URLClassPath.java:1040)
...
*****





They checked directory "C:\Program Files\CA\XCOM\JRE\1.8.0_144\lib\ext\" and there was no file named dnsns.jar.
It had been deleted as part of the install process because it exists in the backup directory created: "C:\Program Files\CA\XCOM_R120BACKUP\JRE\1.8.0_144\lib\ext"

Resolution

XCOM stopped providing a JRE in 11.6 SP03 and onwards and a separate Java 1.8 version needs to be installed: Address Software Requirements
Using the existing XCOM JRE is not possible to run the installer because its install directory including JRE is removed during the upgrade.
This is actually advised on this 12.0 doc page: Upgrade from a Supported Release. See section Prepare for Upgrade:
"In particular, verify that Java 1.8 (64-bit) is installed and set in the path. XCOM Data Transport no longer distributes JRE with the installation, and you cannot use the JRE that was provided with a previous product release."

The current install will need to be ended (Windows Task Manager may need to be used). It is incomplete and effectively bad.

• Follow the steps on this 12.0 doc page to roll back to the 11.6 SP02 version: Uninstall or Roll Back - see section "Roll Back to a Supported Release".
  
  
• Re-run the installer again using a different JRE 1.8 for LAX_VM and select that same JRE when prompted for the java.exe location.