.iss answer file not working with deployment

I have a number of InstallShield executables which have answer files generated for deployment via SCCM2007. Unfortunately the deployment doesn't work. It launches the exe then does nothing and eventually times out. Normally I'd finger the .iss file as badly set up, but it applies correctly when the exe is manually launched, including launching with SYSTEM account from the local CCM Cache.

I've tried several variations on the launch the latest being: %~dp0appname\setup /s /a /s /sms /f1"%~dp0appname\setup.iss"

also %~dp0appname\setup /s

%~dp0centerpoint\setup /s /f1"%~dp0centerpoint\setup.iss"

and others from various net articles, but the result is always the same

Does anyone have any idea why this might be happening?