Install Shield step hangs

[Murrgon]

I have Install Shield professional v11 installed and I am trying to use an InstallShield step to build a setup with it. However, when it gets to that step, the build hangs. I can see IsCmdBld.exe is running in the task manager, but it is occupying zero processor time. I have checked repeatedly all of the paths and they are all correct. What could be causing this?

Thanks