Section 179 only applies to a "Trade or Business".  Does this rental rise to that level?  If so, great.  If not, then 179 is not allowed.

If it does rise to the level of a "Trade or Business", ProSeries automatically assumes a rental does NOT rise to that level.  So you need to add the profit or loss from the rental to line 11 of the 4562 (either by direct entry or if you double click line 11 I think it brings you to a worksheet that has a spot for it).