When creating VOIs for the maps, make sure you name VOIs in SUBJ_AREA format! For example, for mapping multiple injection sessions in the same subject, use SUBJ-SESSION_INJ naming.
Manual definition of ROI/VOI: http://support.brainvoyager.com/functional-analysis-statistics/38-roi-analysis/249-creating-an-anatomically-defined-region-of-interest.html