Calculate Future Value Of Required Minimum Distributions For IRA

I've written the following code. It calculates the future value of required minimum distributions for traditional IRAs. When I enter the function in excel, it drops the last argument. I've tried changing the order of the arguments, and it always drops the last one. The arguments are : marginalTax (marginal tax rate), r (expected return on investment), t (time), begAge (beginning age), RDT (as range -- required distribution table; looks up the percentage required at each age), IRAValueat70 (calcualtes the value of the IRA at 70 years of age)

Function RMD(r As Double, marginalTax As Double, begAge As Integer, t As Integer, RDT As Range, IRAValueat70 As Long)
age = begAge
endAge = begAge + t
Dim holder As Long
Dim RMDnow As Long
Dim RMDall As Long
hat = 70
If endAge < 69 Then
Else
If begAge <= 69 Then
Do While hat < (endAge)
RMDnow = (IRAValue / (Application.VLookup(age, RDT, 2, False)))
RMDnow = (1 - marginalTax) * RMDnow...........................