SQL Data Type Mismatch

[hype261]

So I have a SQL Query I am trying to author and it keeps giving me a Data Type mismatch error which I can't seem to see. Exact error message is Data type mismatch in criteria expression.

Here is the SQL...

SELECT Count(*) AS NumTests, ConvertDate(IssuedDate)
FROM ItasWithCancelledTests
GROUP BY ConvertDate(IssuedDate);

Here is my Function Convert Date

'This method converts a date into a required format
'valid items for the format are:
'Day for day
'Week for week
'Month for month
'Year for year
Public Function ConvertDate(dt As Date) As Date
On Error GoTo Err_ConvertDate
    Dim format As String
    
    'If the person hasn't entered a dateFilter set it to Day
    format = Nz(TempVars("dateFilter"), "Day")
    
    Select Case format
        Case "Day"
            ConvertDate = dt
        Case "Week"
            ConvertDate = DateAdd("ww", DatePart("ww", dt, , vbFirstJan1) - 2, DateSerial(DatePart("yyyy", dt), 1, 1))
        Case "Month"
            ConvertDate = DateSerial(DatePart("yyyy", dt), DatePart("m", dt), 1)
        Case "Year"
            ConvertDate = DateSerial(DatePart("yyyy", dt), 1, 1)
        Case Default
            ConvertDate = Date
            MsgBox "Unable to recognize format"
    End Select


Exit_ConvertDate:
    Exit Function

Err_ConvertDate:
    MsgBox Err.Description
    Resume Exit_ConvertDate
End Function

I have verified that the field IssuedDate is a Date field and if I take away the User designed function then it works properly. Anybody see a problem in my logic here.

[Rabbit]

Nothing jumps out at me as being wrong. Have you tried stepping through the code?

[hype261]

I just figured it out. I had used the function before it a different app so I was pretty sure it worked. The difference between the two was that in my other app the date field was marked as required where in this one the date field is not marked as required. This allowed Access to mark my Date as a Nullable Date where my function is looking for a Non Null Date.