ASP INSERT ฐานข้อมูล.DBF แจ้ง Error Data type mismatch ..!!

<%

 Dim strSQL,objExec
 Set ConnDBF = Server.CreateObject("ADODB.connection")
   ConnStr= "Driver=Microsoft Visual Foxpro Driver; " + _
   "UID=;SourceType=DBC;SourceDB=C:\ASP\Data\Data.DBC;Exclusive=No; Collate=Machine;NULL=YES;DELETED=NO;BACKGROUNDFETCH=NO;"
   ConnDBF.Open ConnStr ,1,3


strSQL = ""
strSQL = strSQL &"INSERT INTO employee "




strSQL = strSQL &"(SSOID,TAXID,NATION,BIRTHDAY) "
strSQL = strSQL &"VALUES "
strSQL = strSQL &"('"&Request.Form("txtSSOID")&"','"&Request.Form("txtTAXID")&"', '"&Request.Form("txtNATION")&"' ,'"&Request.Form("txtTBIRTHDAY")&"') "


Response.write(strSQL)
Set objExec = ConnDBF.Execute(strSQL)
If Err.Number = 0 Then
	Response.write("Save Done.")
Else
	Response.write("Error Save ["&strSQL&"] ("&Err.Description&")")
End If
ConnDBF.Close()
Set objExec = Nothing
Set ConnDBF = Nothing

%>