You have an unruly CA - e.g. "Call VBScript from Embedded Code" and it sometimes works, but sometimes fails and ruins the whole install. In any case the result is not crucial to the successful deployment of the application.
What to do:
In the CA window, select tab 'Properties' and in the 'Processing' drop-down box select 'Synchronous, Ignore exit code'
This way, the msi installation no longer result in the ghastly 1720 msi error code.
We all know that most of the times we have to use MST with vendor's MSI to customise the install process.
We all also know that sometimes the uninstall doesn't remove certain folders or you sometimes need to move a Shortcuts Folder and similar cases.
In these cases we are most likely to use a quick VBScript (objFS.deleteFolder(pathToFolder) with the necessary declarations and variables)
VBScript is very peculiar on whether a folder exists before you can move a file (shortcut) into it or whether you are trying to delete a non-existent folder.
One little slip and we are likely to get 1720.
In cases like this, utilize the option depicted in the 'What to do' section above.