Trouble With Datetime Insert And Update

I am trying to Insert or Update a record in MSSQL with a datetime variable which is modified using the DateAdd function.

Basically, I have a table of Coupons which need to expire 'x' days in the future. When I use GetDate() for the Issue Date, I have no problems. But then, when I use DateAdd to return a date in the future, I can not Insert or Update this result into the record.

I get various errors having to do with type mismatch or function not found, etc.

Can you see what I might be doing wrong?

Here's the code snippit:
<%
if(Recordset2.Fields.Item("SerialNo").Value <> "") then UpdateExpire__SerNo = Recordset2.Fields.Item("SerialNo").Value
if(DateAdd("d",2,Now) <> "") then UpdateExpire__XD = DateAdd("d",2,Now)
%>
<%
set UpdateExpire = Server.CreateObject("ADODB.Command")
UpdateExpire.ActiveConnection = MM_FreeVB_STRING
UpdateExpire.CommandText = "UPDATE dbo.Coupon SET ExpireDate = " + Replace(UpdateExpire__XD, "'", "''") + " WHERE SerialNo = " + Replace(UpdateExpire__SerNo, "'", "''") + ""
UpdateExpire.CommandType = 1
UpdateExpire.CommandTimeout = 0
UpdateExpire.Prepared = true
UpdateExpire.Execute()
%>

This produces this error:

Microsoft OLE DB Provider for ODBC Drivers error '80040e14'

[Microsoft][ODBC SQL Server Driver][SQL Server]Line 1: Incorrect syntax near '12'.

And it errors at the UpdateExpire.Execute() line.

The code was generated by Dreamweaver.

Thanks.

Lance