1. The sample code was from a Run Script step. If your script code is in a custom user action, macro references are not automatically expanded and Application.ExpandMacros is needed.
2. Use the same log file for both the parent and child project.
3. For custom actions, the return value of the vbld_BuildStep method indicates success/failure.
http://www.visualbuild.com/Manual/userdefaction.htm
vbld_BuildStep = Builder.RunProgramEx(...
Not sure what you're trying to achieve, but some possibilities:
1) Generate and display an HTML report from the XML build log rather than depending on a GUI VBP instance getting launched.
http://www.visualbuild.com/Manual/tr...mlogaction.htm
2) Just use a VisBuildPro Project action instead of a custom user action.
http://www.visualbuild.com/Manual/vi...projaction.htm
3) Passing macros via the command-line is fairly straightforward if you must invoke the GUI. You can also use other methods to pass the values (for instance, store in temporary macros and save the macros file in the caller, then load the temp macros in the callee).