Yep, you're right - at first look I didn't really inspect your code. This is a problem:

VB Code:
  1. mArrDate = Me.dtpArrive.Value

  2.         mDepDate = Me.dtpDepart.Value

  3.         Do While mArrDate <= mDepDate

  4.             If mArrDate.DayOfWeek = DayOfWeek.Sunday Or mArrDate.DayOfWeek = DayOfWeek.Monday Or mArrDate.DayOfWeek = DayOfWeek.Tuesday Or mArrDate.DayOfWeek = DayOfWeek.Wednesday Or mArrDate.DayOfWeek = DayOfWeek.Thursday Then

  5.                 mNumWeekdays += 1

  6.             End If

  7.         Loop

If mArrDate is today and mDepDate is a week from today, your Do...While loop will never end.

You're probably going to need to rethink and recode.