Populate List Boxes When A Form Field Changes Value

I have three list boxes on a form (lstSubjectName, lstTargetGrName, lstCountryName). The list boxes are populated from queries
based upon tables that have a many-to-one relationship to the main table. The
queries are the following:

SELECT tblProjectSubject.ProjectID, tblProjectSubject.SubjectName
FROM tblProjectSubject
WHERE (((tblProjectSubject.ProjectID)=[Forms]![frmViewPro]![ProjectID]))
ORDER BY tblProjectSubject.SubjectName;

SELECT tblProjectTargetGr.ProjectID, tblProjectTargetGr.TargetgrName
FROM tblProjectTargetGr
WHERE (((tblProjectTargetGr.ProjectID)=[Forms]![frmViewPro]![ProjectID]))
ORDER BY tblProjectTargetGr.TargetgrName;

SELECT tblProjectCountry.ProjectID, tblProjectCountry.CountryName
FROM tblProjectCountry
WHERE (((tblProjectCountry.ProjectID)=[Forms]![frmViewPro]![ProjectID]))
ORDER BY tblProjectCountry.CountryName;

The form is based on the main table (tblProjects).
I want to re-populate/update the list boxes when the ProjectID on the form
changes. I have tried to use a macro (ProjectID_AfterUpdate) for requery of
the list boxes, but can't get it to work.
Any other solutions? Thanks.
Niels