UDFs evaluating to #NAME

I have a problem I cannot for the life of me work out why there is a problem.

I have the following function.

Function WhatYear(pdate As Date)
'Application.Volatile
Dim year_count As Integer
Dim answer As Integer
Dim date_start As Date
Dim date_end As Date

year_count = 1982
answer = 0

While answer = 0
    date_start = DateSerial(year_count, 4, 6)
    date_end = DateSerial(year_count + 1, 4, 5)
    If pdate >= date_start And pdate <= date_end Then
        WhatYear = year_count
        answer = 1
        Else
        year_count = year_count + 1
    End If
Wend
year_count = 1982
answer = 0
End Function

It works out what tax year a date falls in. It has worked perfectly well. When it is downloaded from the net though it opens with the cell showing #NAME. If I use recalc or anything similar it doesn't change. The only way it comes up with an answer is if I edit and exit the cell. After that it works perfectly. Is there something wrong with this code? Or is it just something odd? TIA

Rorya - The code was written then the formula used. It is now on downloading and reopening that the problem arises. How would I force a recalc using a piece of script?

dominicb - that is kind of the problem. It works until it has been round the internet and back. Just wondered if there was soemthgin that wasn't technically correct in it that would cause the problem.

It is. There's no duplication of UDF names, no modules named the same, no ranges named the same.