I'm not sure what the problem is here but I'll show you a little trick that you can use to find out.
Have your editor open. Fill in your form and post it. If you get a Page Cannot Be Displayed, select all of the code on your page, delete it and type a single character on the page. Refresh your page and you should see that single character. Then do a Ctrl + Z in your editor to put the code back into the page. Save it and refresh the page again. This will then give you exactly what the error is and possibly a line number.
I don't use the UPDATE method in classic asp. Here is how I would execute your code.
This code executes fine. I tried it.
Code:
<%
DIM objRS, objConn, strConn
strConn = "Driver={SQL Server}; server=myserver;Database=mydatabase; UID=myid; PWD=mypw"
Set objConn = Server.CreateObject("ADODB.Connection")
objConn.Open strConn
SQL = "Insert into tbltest (Email, FirstName, LastName, Comments, DateContacted) VALUES ('" & Request("Email") & "', '" & Request("FirstName") & "', '" & Request("LastName") & "','" & Request("Comments") & "', '" & Date() & "') ;"
Set objRS = objConn.Execute(SQL)
objConn.Close
Set objConn = Nothing
%>
Hope this helps.