Type mismatch: '[string: ""]' error when sending form

[mr_nabo]

Hi,

I have no clue about asp and have been asked by a client to create a registration form.

Totally crude, I know, but I've created an image of a calculation question and I'm getting users to add the numbers together and checked against an asp script I have written.

However, when I use it, it gives me the error:

Microsoft VBScript runtime error '800a000d'
Type mismatch: '[string: ""]'
/booking-form/sendit.asp, line 97 

Here's the code I've written and the HTML form part that's relevant. Any ideas?

Thanks

HTML

...

<img src="what-is.gif" alt="img-q" width="87" height="19"/><br />
  <input type="input" name="captcha" value="" /><br /><br />
  <input type="submit" name="submit" value="Submit" class="submit">

...

ASP

<%
' send email if captcha = 12 
Dim captcha
captcha = Request.Form("captcha")
if captcha = 12 Then
Dim mail
Set mail = Server.CreateObject("CDONTS.NewMail") 
mail.To = EmailTo
mail.From = EmailFrom
mail.Subject = Subject
mail.Body = Body
mail.Send
' redirect to success page 
Response.Redirect("ok.htm?" & EmailFrom)
Else
Response.Redirect("error.htm?" & EmailFrom)
End If
%>

[bmcgee]

If Trim(captcha) = "12" Then