This error indicates that there is an empty executable path for an application mapping on a website, application, or virtual directory that is included in the project. This value cannot be empty. Note that the IDE will not allow an application mapping to be added that does not contain an executable path. To verify that an application mapping is present in the project with an empty executable path, go to the IIS view and look at all application mappings present for any websites, applications, or virtual directories that are listed in the view. Either remove or correct any mappings that do not have a value for executable path.
Also note that if the executable path is a property reference ([PROPNAME]) and this property has no value at runtime, the executable path will resolve to an empty value which will also cause this error. If a property is used for the executable path in an application mapping, the property referenced needs to contain a value to avoid this error.
Josh Stechnij - Software Engineer - Flexera Software: InstallShield Team