how to convert VBA #date# format to C# code?

[Rock]

Hi,all:

how to convert VBA #date# format (ex: #2004/3/6#) to C# code ?
here are vba code :
Dim objUserPerm As Office.UserPermission
Set objUserPerm = ActiveWorkbook.Permission.Add("(e-mail address removed)",
msoPermissionRead + msoPermissionEdit, #12/31/2005#) a to c# ??
I don't know how to convert this code to C#? and I have already try
it use DateTime format, but it happen argument error. anyone have the
same problem ? thank you.
Rock