Most software packages that require ISScript.msi actually include the file inside their own installation media. Before downloading files from unknown websites, check your installer source:
Ensure that the Windows Installer service is active and running in the services.msc manager. isscriptmsi new download
isscript.msi is a component of the InstallShield installation software, widely used by software developers in the early to mid-2000s. Most software packages that require ISScript