Software Management Solution Plug-in Install or upgrade fails. Exit code=1638
There are registry keys left over that cause Windows Installer to think another version is already installed.
We used a Run Script task to remove the registry keys that were causing problems. The following script may need to be changed based on the GUID of the old Plug-in install.
First, do a search in the registry for "Software Management Solution" under the HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall and Installer keys. The guid of the folder where the string is found (confirm it is the plug-in in the name) and use that in the scripts.