you should not exceed 64k vertices on one object in ZModeler. You should not exceed 64K vertices in total on all parts related to any single material (overal vertices limit is higher, when per-material usage is kept below 64K). If the second limitation is your case, create a copy of hardly-used material and assign this copy onto half of polygons that use original material.
game crash can have various reasons, model size + base value is the most common cause, but not the only. In particular, FAILURE_3 is more likely to messed hierarchy (missing original parts/collisions that game expected to find in your model, but failed to find them).