When a user attempts to upload a file over 30 MB, the upload instantly fails with a 404 (Page Not Found) error. No other error information is received.

If your webserver is running URLscan version 2.5 or above, this problem is most likely caused by a default setting in URLScan which limits the size of HTTP requests to 30 MB. The upload fails instantly because IIS cuts the connection as soon as it checks ContentLength header of the HTTP Request.

You can easily remove this limitation in the following manner:

1. Navigate to the configuration file for URLscan. This is usually is usually located in the directory C:\Windows[or WINNT]\system32\inetsrv\urlscan.
2. Open the file "urlscan.ini"
3. Change the setting of MaxAllowedContentLength to the maximum number of bytes you wish to allow. By default, URL restricts upload size to 30 MB:
   
   

   MaxAllowedContentLength = 30000000 

4. Restart IIS by typing "iisreset" at the command prompt