Happens when you are multitasking 3 projects!

Sub SumSelectedCells()
aRandomNumber = 1
CellsToSum = Selection.Address
LastInRange = Selection.Rows.Count
vSum = WorksheetFunction.Sum(Range(CellsToSum))
Range(CellsToSum)(LastInRange).Offset(0, 2).Value = vSum / aRandomNumber
End Sub