Project macros are specific to a given project (.bld file). They are not automatically passed to project B when called from project A. You can pass them as temporary macros to a chained project using the Parameters tab of the VisBuildPro Project action.
Temporary macros are specific to a given VBP instance and are not persisted to disk. They are created by passing macro values on the command-line, a Set Macro action, and by various actions when a step of that action type is built (i.e., COPY_COPY_COUNT, PROCFILES_FILENAME, etc.), prompting for undefined macros, etc., and usually deleted at the end of a build. They have a higher precedence than project macros (a temporary macro X will be used over project macro X).
http://www.visualbuild.com/Manual/macrostab.htm