Date Comparison From Siebel

I have an issue in comparing 2 dates. It gives a data type mismatch error

Private Sub TextBox12_Click()
Dim siebApp As SiebelWebApplication
Dim siebBusObj As SiebelBusObject
Dim revBC As SiebelBusComp
Dim isRecord As Boolean
Dim sRep As String
Dim sCompany As String
Dim sLocation As String
Dim sStep As String
Dim sProb As String
Dim sDate As String
Dim CurDate As Date
Dim RetDate As Date
Dim datmins As Integer
CurDate = Now()
Const DateCol = 9
RetDate = ThisWorkbook. Sheets("Users"). Cells(DateCol)
r = ThisWorkbook.Sheets("Users").Cells(65536, 1).End(xlUp).Row 'Get next blank row
ThisWorkbook.Sheets("Users").Cells(r, DateCol) = CurDate....................

I have highlighted in bold where i do the date comparison. Here are the date formats [Last Updated] = 2002-11-08 13:19:03.000

[RetDate] = 2/13/2008 15:59:18