Oops, interaction() returned a single value in stead of a tuple (I thought that bug was loooong fixed??!?).
diff --git a/Mac/scripts/BuildApplication.py b/Mac/scripts/BuildApplication.py
index bf44ebd..e9884a4 100644
--- a/Mac/scripts/BuildApplication.py
+++ b/Mac/scripts/BuildApplication.py
@@ -112,11 +112,10 @@
 
 def interact(scriptname):
 	if PPC_ONLY:
-		return 'pwpc'
+		return 'pwpc', 1
 	d = Dlg.GetNewDialog(DLG_ID, -1)
 	if not d:
-		print "Can't get DLOG resource with id =", DLG_ID
-		return
+		raise "Can't get DLOG resource with id =", DLG_ID
 	d.SetDialogDefaultItem(OK_BUTTON)
 	d.SetDialogCancelItem(CANCEL_BUTTON)
 	Dlg.ParamText(scriptname, "", "", "")