Software Deployment

On Win7 x64 I've got an old Installshield setup.exe that installs successfully under system context via SCCM or PSEXEC when UAC is set to Never Notify. If UAC is set to anything higher than Never Notify the install errors out with error 1628. It was my understanding that the System account is not affected by UAC, however this does not seem to be the case in this situation. Any ideas what could be causing this or how to resolve it without having to adjust UAC settings?

One thing I've noticed is that when I look at the setup.exe in a resource viewer, the exe's manifest shows that the RequestedExecutionLevel is set to "highestAvailable". I'm not sure of this is relevant to the issue.

Appreciate any advice/ideas.

EDIT:

I've found a solution. Setting the environment variable __COMPAT_LAYER to RunAsInvoker and then running the setup works. The setup now runs under system context with no error.