That at least tells us it's something that's gone wrong on the system rather than the installer itself, which is useful to know.
If anyone who is still seeing this problem wants to make and send us some Process Monitor logs we can see what they indicate. In the past we've seen this issue caused by part of the installer being killed the moment it runs, probably by antivirus (but we aren't sure). But it also seems that InstallShield can produce similar error messages for various different problem causes, so it may be different causes on different PCs. We're happy to look through logs to see if we can help with a particular machine, or if it points to something we might be able to change at our end to cope with whatever is going wrong.
Knowing which antivirus and registry cleaners (and similar) people experiencing this have could also be useful, in case there is a pattern. (Sometimes those tools can cause problems even when disabled, since they sometimes still install hooks but configure them to do less rather than remove them.)