Processing Formdata To Text File

I have a very simple form with text fields which I would like to append the data to a text file.

Here is the code I have written, but I just keep getting an HTTP 500 - Internal server error

If I remove all the code and just leave the response.write at the end then that works, so ASP is working.

I am very new to ASP, so have no idea where to start.

<%
'declare varibales to hold info
dim email,firstname,subject,comments,separater,textfil epath
const ForAppending = 8
separater = "|"
'sub to call to add to text file
sub addToTextFile (byval textdata)
set FSO = Server.CreateObject("Scripting.FileSystemObject")
set myFile = fso.OpenTextFile(textfilepath, ForAppending, True)
myFile.Writeline textdata
myFile.Close
set FSO = Nothing

'grab form fields
email = request.form ("Email")
firstname = request.form ("FirstName")
subject = request.form ("Subject")
comments = request.form ("Comments")

'add to text file
data = email & separater & firstname & separater & subject & separater & comments
textfilepath = Server.MapPath( "results.txt" )
addToTextFile data

Response.Write ("<p>Thank you your response.</p>")
%>