Code to have Outlook VBA read an Excel file (cell with a date), then have Outlook send a reminder on that same date.

Ok here is the code, all below needs to be copied in to "ThisOutlookSession" code pane under [Tools > Macro > Visual Basic Editor] in Outlook.
Note that you will need to reference the "Microsoft Excel Object Library" for it to work. Also as this code currently stands, you need to delete the old task for it to create a new one, this could be modified so it will create the new one if the date is different. The code will run everytime Outlook starts (make sure Macros are enabled).

'------- Start Copying Below Here --------

' this is the subject to be put in the task
Private Const mTaskSubject As String = "Task From Excel"

Private Sub Application_Startup()
    ' check task does not already exists and create if not
    If Not ExcelReminderExists Then
        Call CreateExcelReminder("C:\SourceFile.xls")
    End If
End Sub

Private Sub CreateExcelReminder(sFilePath As String)
    ' you will need to add a reference to "Microsoft Excel" object library in the tools>reference menu.
    Dim oXlsApp As Excel.Application
    Dim oWkBk As Excel.Workbook
    Dim oWkSt As Excel.Worksheet
    Dim dtDate As Date
    Dim oTask As Outlook.TaskItem

    On Local Error GoTo ErrorTrap

    ' create hidden copy of excel
    Set oXlsApp = CreateObject("Excel.Application")
    If oXlsApp Is Nothing Then GoTo CleanUp
    oXlsApp.Visible = False
   
    ' load specified file
    Set oWkBk = oXlsApp.Workbooks.Open(sFilePath, False, True, , , , , , , , , , False)
    If oWkBk Is Nothing Then GoTo CleanUp

    ' get required worksheet
    Set oWkSt = oWkBk.Worksheets(1)
   
    ' read the date from the excel file (this presumes it is in cell 1A)
    dtDate = oWkSt.Cells(1, 1)
   
    ' make sure date includes time of 8:00 am
    dtDate = CDate(Format(dtDate, "dd mmm yyyy") & " 8:00am")
   
    ' create a new task and set properties for reminder etc.
    Set oTask = Application.GetNamespace("MAPI").GetDefaultFolder(olFolderTasks).Items.Add
    With oTask
        .Subject = mTaskSubject
        .ReminderSet = True
        .ReminderOverrideDefault
        .ReminderTime = dtDate
        Call .Save
    End With

CleanUp:
    Set oTask = Nothing
    Set oWkSt = Nothing
   
    ' close woorkbook if still open
    If Not oWkBk Is Nothing Then
        Call oWkBk.Close(False)
        Set oWkBk = Nothing
    End If
   
    ' close excel (if still open)
    If Not oXlsApp Is Nothing Then
        Call oXlsApp.Quit
        Set oXlsApp = Nothing
    End If
    Exit Sub

ErrorTrap:
    MsgBox "Error: #" & Err.Number & vbCrLf & Err.Description
    Resume CleanUp
End Sub

Private Function ExcelReminderExists() As Boolean
    ' search for a task with our subject and return True if found
    With Application.GetNamespace("MAPI").GetDefaultFolder(olFolderTasks)
        ExcelReminderExists = Not (.Items.Find("[Subject] = " & mTaskSubject) Is Nothing)
    End With
End Function

'------- Stop Copying Above Here --------

Many Regards, Jomac.