This may be due to non-numeric values being entered in the room's Capacity in Core. To correct this:
  1. Go to Core > School > Buildings.
  2. Expand the Building.
  3. Click the Pencil icon next to a room with a non-numeric value in the Capacity (i.e. 10+2, 11-1, etc.).
  4. Change the capacity to an integer value (i.e. instead of 10+2, select 12).
  5. If desired, add the original capacity value to the Notes section for the Room.
  6. Click Save.
  7. Repeat for any other affected rooms.