We've run into a few applications that wouldn't install properly via SMS if a non-admin was logged onto the system when the package got deployed. If an administrator was logged on or if no one was logged on at all everything worked great. This seemed a bit strange because everything should run as the local System account, right? Well, this isn't necessarily true in the case of a MSI created with InstallShield that utilizes ISScript.
When ISScript gets deployed, it sets its DCOM permissions to Interactive User. So when the MSI runs, it is possible that certain components of the install routine will try to run as the logged on user--not as System.
Anyway, you can fix the issue by deleting a few registry values. The problem is that if ISScript ever gets reinstalled it will set itself back to run as Interactive User. And each version of ISScript has a different DCOM app that needs to be checked for the problem. It looks like ISScript versions 7, 8, and 9 all have the problem and one of our packagers is thinking that version 10 does as well. Not sure about 10.5 or 11 yet.
Anyway, someone already posted a really good article on the problem if you care to read more on it and exactly how to fix the issue if you run into it.