Duplicate entries in Add/Remove Programs, not good.
Usually the duplicate entries are caused by re-installing a program, or installing a newer version of a program, without using Add/Remove programs to uninstall the old one first.
Example : Entry for Adobe reader 9.5 and 9.5.1 in Add-Remove Programs however latest version of application is available to users.
The cause of this behavior may be a result of the previous version being installed per machine and the upgrade was installed per user.
If duplicate entries appear in the Control Panel, the ALLUSERS property for the second installation is not the same as in the first installation.
To determine if the .MSI files are per-machine or per-user installations, generate log files during the installations. To create a log file, use the following command line option:
msiexec.exe /i "C:\Program Files\My MSI.msi" /L*v "C:\Program Files\InstallLog.txt"
Compare the two log files to determine if the ALLUSERS property is the same for each installation. If the ALLUSERS property is different, go to the Product tab in Setup Editor and click Properties. Locate the ALLUSERS property and set the property equal to 1 or 2.