Hi @rparveez,
There are some additional registry entries used by the installer that are located at
C:\Program Files (x86)\Zero G Registry\.com.zerog.registry.xml
In case this file contains a FreeMASTER entry in <products> list the, back up the file and remove it from the disk. Relaunch the installer.
Note: If FreeMASTER is the only product it the mentioned registry file, it is safe to completely remove the file (without backup) as it will be recreated automatically during installation process.