Problem with thumbnails

Does those same errors happen in the demo page? http://www.ckfinder.com/demo

It's very strange to get a javascript error, have you modified anything else besides the config.asp file?
Can you provide a link to test the error?

Follow this steps:

Save this file in your ckfinder folder as web.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.web>
    <compilation debug="true" />
    <customErrors mode="Off" />
  </system.web>
</configuration>

Now load CKFinder, get ready to upload an image, but at that moment edit config.asp and set

CKFinder_Debug = true

Then press the upload button.

Now it should provide the full asp.net error message

doing a live-resize will still need the safety checking so only thumbs of uploaded pictures are requested, and it would have a penalty on the server performance if it has to generate the same thumbs over and over again.

I'll try to write later some code to help you debug the problem

You are thinking about your case, but what about other people that have hundreds of pictures in a single folder. At 25 per second (and if they aren't big as you state) that means several seconds with the server scaling the same images over and over again. And now imagine that there are several users at the same time working with that server...

The privacy is again just a point of view: imagine a situation where each user is allowed only to see his pictures, with your live-resizing without any extra check it would be possible to get the thumbnails (and you can request them at big dimensions) of other people's pictures.

About your problem:
open core/connector/asp/loopback.aspx and in line 48 change it to add the name of the tempfile:

         
Response.Write( "<h1>403 - Forbidden</h1>" & tempFile);

Also, in Utils\fileSystem.asp go to line 429 and comment out that line so the temp file isn't deleted

      
'DeleteFile tempFilePath

Now try to do the upload again, it should show the name of the file that is being tested as a token, check if that file exists.
If it exists, then it means that the asp.net doesn't have enough priviledges to read that file (although it should have raised an exception and then it could have suggested to use the CKFinderTempPath setting in the config.asp and web.config files.

That path looks like something specific to asp.net

I've checked in a winXP installation and I've seen the same problem. As I suggested, I've disabled the deletion of the temp files and I can find them under "C:\WINDOWS\Temp", but the asp.net pages are looking for them in C:\documents and settings\machine\ASPNET\local configuration\temp
so good to have a temp folder in the system!

The solution as I have suggested previously is to use CKFinderTempPath and that way you are sure that both environments are looking at the same place.

Or if you are totally sure that there are no problems about requesting the asp.net pages from anywhere, change the loopback.aspx to

   private bool CheckIsLocalRequest()
   {
      return true;
   }

Have you verified that the ckfindertemp files are being created in that folder?
And does the message from asp.net point to that same folder?