Dear Who Ever

I created a separate aspx page as a booking request form for a hotel group
The function of the form is to collect booking requirements from the end user
Fields like contact details, destination, arrival date, departure date etc.
On submit an email with the requirement details is forwarded to the relative department
This is my code:

Dim objMessage As Object

Dim FirstName As String = e.Values.Item("FirstName")

Dim Surname As String = e.Values.Item("Surname")

Dim Email As String = e.Values.Item("Email")

Dim Telephone As String = e.Values.Item("Telephone")

Dim City As String = e.Values.Item("City")

Dim Destination As String = e.Values.Item("Destination")

Dim Adults As String = e.Values.Item("Adults")

Dim Children As String = e.Values.Item("Children")

Dim Toddlers As String = e.Values.Item("Toddlers")

Dim Arrival As Date = e.Values.Item("Arrival")

Dim Departure As Date = e.Values.Item("Departure")

Dim SpecialRequirements As String = e.Values.Item("SpecialRequirements")

objMessage = Server.CreateObject("CDO.Message")

objMessage.Subject = "Accommodation Enquiry"

objMessage.From = "tino@ecbroker.co.za"

objMessage.To = "tino@ecbroker.co.za"

objMessage.HTMLBody = "

Kat Leisure Accommodation Enquiry

" _

& "Date of Enquiry: " & Today.ToLongDateString _

& "

Contact Details

" _

& "First Name: " & FirstName & "
" _

& "Surname: " & Surname & "
" _

& "Email Address: " & Email & "
" _

& "Telephone No.: " & Telephone & "
" _

& "Nearest City: " & City _

& "

Accommodation Requirements

" _

& "Destination: " & Destination & "
" _

& "Number of Adults: " & Adults & "
" _

& "Number of Children: " & Children & "
" _

& "Number of Toddlers: " & Toddlers & "
" _

& "Date of Arrival: " & Arrival.ToLongDateString & "
" _

& "Date of Departure: " & Departure.ToLongDateString & "
" _

& "Special Requirements: " & SpecialRequirements

objMessage.Send()

objMessage = Nothing

This worked fine and I have test-installed it numerously with different versions of dnn
434, 455, 462

When it came to installing it on the real site I got the following error:
The "SendUsing" configuration value is invalid.
This happens on objMessage.send()

If I run the aspx page in debug mode everything works fine and the mail is delivered
If I test smtp settings in Host settings - success
Going back to a test version gives me the same error as described above
So now I cant get it to work in dnn at all
Please can u help?