error type mismatch vb6

getting an error "By reference mismatch" when trying to call this function:

Function DetermineNextTaskTime(dteTaskTime As Date) As String
Dim dteTaskTimeTom As Date
Dim dteTimeNow As Date
Dim lngDifference As Long
Dim lngHours As Long
Dim lngMinutes As Long

dteTimeNow = TimeValue(Now)
' This is set up for a 9AM task
'dteTaskTime = TimeValue("9:00") ' assumes military time
dteTaskTime = TimeValue(dteTaskTime) ' assumes military time

If dteTimeNow > dteTaskTime Then
    ' Format a date+time value that represents the task time tomorrow
    dteTaskTimeTom = Format(Now + 1, "short date") & " " & dteTaskTime
    lngDifference = Abs(DateDiff("s", dteTaskTimeTom, Now))
Else
    lngDifference = DateDiff("s", dteTimeNow, dteTaskTime)
    lngHours = (lngDifference \ 60) \ 60
    lngMinutes = (lngDifference - (lngHours * 60 * 60)) \ 60
End If

lngHours = (lngDifference \ 60) \ 60
lngMinutes = (lngDifference - (lngHours * 60 * 60)) \ 60
'MsgBox "Task due in " & lngHours & " Hours and " & lngMinutes & " Minutes"
DetermineNextTaskTime = lngHours & lngMinutes
End Function)

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gNewTime = "09:00 AM"
 .TextMatrix(LastRow, mgrdNxtDueDate) = DetermineNextTaskTime(gNewTime

what is wrong ?