InstallAware

We release our Application exe for every 2 months with an increase version number
Eg:
Hello.exe  Version 12.1.1.0
Hello.exe  Version 12.1.2.0 (This is not a patch release and after installing this version, user won’t uninstall the previous version)
Hello.exe  Version 12.1.3.0 (This is not a patch release and after installing this version, user won’t uninstall the previous version)

Our client can install n number of application versions and they select a particular application version at run time based on their requirement.
The problem is, I am unable to install “Hello.exe (Version 12.1.1.0)”, If the PC is already installed with the version “Hello.exe (Version 12.1.2.0) “. I am struggling to fix this problem.

Any help would be much appreciated.

I am unable to install “Hello.exe (Version 12.1.1.0)”, If the PC is already installed with the version “Hello.exe (Version 12.1.2.0) “

What do you mean exactly? Do you get an error or what?

It is showing a dialog box with text "error" during Main Installation.

But it's not clear when the error occurs exactly.

Does it happens during "Apply Install" command execution?
If true, and assuming your installer is based on Windows Installer engine, you may try to run a logged installation to see if such error gets reported by the generated log file.

To execute a logged setup, use the following command line:
<setup.exe> /l=<path to logfile>

You are right, Installation fails during "Apply Install". My installer is based on Windows Installer engine

I have followed your suggestion and logged the error
errlog-full.txt has full log information - It appears to be related to error 1603

I have also gone through the below topic
viewtopic.php?t=10595

cleared %TEMP% folder - not solved the issue
Run as Admin - not solved the issue
changed the install location C:\Users\Public\Documents - not solved the issue

Do you have any further suggestions to clear this issue?

Error 1603, it's is also caused when a file or a component is being held in use by another process, and probably your installer, it's trying to install "something" which is currently in use.

Due the fact that your install only fails when it tries to update a previous existing version, it may be possible that this previous version doesn't get uninstalled correctly, or that this gets partially un-installed. As for example a service, which may be in use when this is going to be removed.