I think you have made up some of your own VBA syntax there

The immediate problem you have mentioned is the use of Set
The line should be simply iCounter = 0, but then you will find other problems. Use the following function instead, which will add weekdays to a given date - here Today, so add 15 days to that and you get 11th August. The first macro shows how to call the function.
Code:
Sub Macro1()
Selection.TypeText Format(DateDue(Date, 15), "mm-dd-yyyy")
End Sub
Public Function DateDue(ByVal vDate As Date, ByVal iDays As Variant) As Variant
'Graham Mayor - http://www.gmayor.com - Last updated - 14 May 2017
'Add weekdays to date - from Monday if date falls at weekend
Dim iCount As Integer
DateDue = Null
If IsNull(vDate) Or IsNull(iDays) Then
GoTo lbl_Exit
End If
Select Case Weekday(vDate)
Case Is = 1 ' Sunday
vDate = DateAdd("d", 1, vDate)
iCount = 0
Case Is = 7 ' Saturday
vDate = DateAdd("d", 2, vDate)
iCount = 0
Case Else
iCount = Weekday(vDate) - 2
End Select
iDays = iDays + iCount
vDate = DateAdd("d", iCount * -1, vDate)
DateDue = DateAdd("d", iDays Mod 5, DateAdd("ww", Int(iDays / 5), vDate))
lbl_Exit:
Exit Function
End Function