Here's my version of this function.

VB Code:
  1. Function DaysInMonth(MthNum As Integer, YrNum As Integer) As Integer

  2. Dim dtTemp As Date

  3.     

  4.     dtTemp = DateSerial(YrNum, MthNum, 1)

  5.     DaysInMonth = DateAdd("M", 1, dtTemp) - dtTemp

  6. End Function