Some component of the XCOM uninstall process did not complete successfully. e.g. one possible root cause is still having this registry key in existence after XCOM was uninstalled: "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\CA XCOM Data Transport r11.6 SP02 (64-bit)"

Release : 11.6
Component : CA XCOM Data Transport for Windows

There is a cleanup utility designed to resolve all problems with incomplete uninstalls for various XCOM versions which prevents a new install from executing.
The utility can be accessed here: ftp://ftp.broadcom.com/pub/xcom/xcpcnt/Uninstall%20program/
Note: Per the readme.txt file:
To cleanup 32-Bit versions of XCOM, use cleanup32.zip and file xcomunin32.exe.
To cleanup 64-Bit versions of XCOM, use cleanup64.zip and file xcomuni64.exe.
For Windows Server 2008 SP02, use xcomunin64.exe utility irrespective of XCOM version.

After the relevant xcomunin*.exe file has completed and the server has been restarted the XCOM install should then proceed without any problems.

NOTES:
If the install is still blocked after running the cleanup utility then running the following commands to delete 2 more registry keys may be needed to resolve the problem (has been reported when the previous install was r11 32-bit):
REG DELETE "HKEY_LOCAL_MACHINE\SOFTWARE\ComputerAssociates\XCOM\RemoteSystemsTS\" /f
REG DELETE "HKEY_LOCAL_MACHINE\SOFTWARE\ComputerAssociates\XCOM\" /f  

1. The latest XCOM for Windows 11.6 service pack SP03 has been enhanced to use similar cleanup techniques to detect any remnants from the previous installation and prompt the user to choose whether to clean those up and proceed with the installation:
CA XCOM DATA TRANSPORT FOR WINDOWS 11.6 SERVICE PACKS > Release Notes > Enhancements for Service Packs - see "Enhancements for Service Pack 11.6.03 > Installation Improvements"