Ringrazio tutti quelli che generosissimamente mi aiutano.
Ora ottengo un errore da questo codice, alla riga 67 (da me evidenziata). L'errore è il seguente:

Type mismatch
/editpost.asp, line 67
codice:
<%@LANGUAGE = "VBSCRIPT" %>
<%Option Explicit%>

<%
Dim rs, strSQL, postTitle, postText, postPublished, postID, nopost, isError

if Request.Form("btnPost") > "" Then
	postTitle = Replace(Request.Form("postTitle"), "'", "''")
	postText = Replace(Request.Form("postText"), "'", "''")
	postID = Request.Form("postID")
	
if Request.Form("postPublished") = 1 then
		postPublished = 1
	else
		postPublished = 0
	end if
	
if postTitle > "" and postText > "" Then
					strSQL = "UPDATE tblPosts SET postTitle = '" & postTitle & "', postText = '" & postText & "', postPublished = " & postPublished & " WHERE postID = " & postID
										
					conn.execute(strSQL)
					
					response.redirect "entries.asp?edit=true"
else

			isError=true
	end if
	
else

		postID = Request.QueryString("postID")
		set rs = Server.CreateObject("ADODB.Recordset")
		strSQL = "SELECT * FROM tblPosts WHERE postID = " & postID
		rs.open strSQL, conn
		if not rs.EOF then
				postTitle= rs("postTitle")
				postText= rs("postText")
				postPublished= rs("postPublished")
		else
				nopost = true
		end if
		rs.close
		set rs = nothing
end if %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Blog Admin: edit a post</title>
<link href="stilemarghbis.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div id="content">
  <% if not nopost = true then %>
  <% if isError = true then %>
  <p class="error">You must give your blog post a title and complete the entry
    to submit the form</p>
  <% else %>
  

Edit your post</p>
  <% end if %>
  <form method="post" action="editpost.asp">
    


      <label for="postTitle">Title:</label>
      <% if isError = true and postTitle="" then %>
      <span class="error">Please add a title
      <% end if %>
      

      <input type="text" name="postTitle" value="<% postTitle %>" />     
    </p>
    


      <label for="postText">Your entry:</label>
      <% if isError=true and postText="" then %>
      <span class ="error">Please add your entry
      <%end if%>
      

      <textarea name= "postText" id="postText" class="txtlarge" cols="40" rows = "10" ><% = postText %>
</textarea>
    </p>
    


      <label for ="postPublished">Publish?</label>
      <input type="checkbox" name="postPublished"
id= "postPublished" value="1" <% if postPublished =true then %>checked = "checked"<% end if %> />
    </p>
    


      <input type="hidden" name ="postID" id="postID" value =" <% postID %>" />
      <input type="submit" name="btnPost" id="btnPost" value="edit Entry" />
    </p>
  </form>
  <% end if
set conn = nothing
%>
</div>
</body>
</html>