I gave up trying to get the Task Scheduler to open Access files. I use VB Script files. Here is some code that you can use to create a VBS file using your text editor. Just change the extension to .VBS
Code:
Option Explicit
Dim oShell
'open the Access file
Set oShell = CreateObject("WScript.Shell")
oShell.Run """C:\Program Files (x86)\Microsoft Office\Office14\MSACCESS.EXE"" ""C:\FolderName\FileName.accdb"""
With that, you can simply tell the Task Scheduler where the VB script file is (somewhere locally with rights) using the file picker provided by the task scheduler. I guess you can add your switch after the accdb extension too.