Large enclosures in browsers simply take a long time to upload. There may be many reasons why you may be experiencing timeouts or long delays.
The larger the enclosure, the longer the upload time. Network congestion and the speed of your connection all play a roll.
Your network and/or firewall may have limitations on the size of an upload, whether you are allowed to upload at all, and the length of time a connection is allowed before it is forcefully broken.
If on NT and running as a CGI, see elsewhere in this folder for tips.
Large uploads will do better if you are running Web Crossing in Direct Web Service mode, bypassing the overhead of CGI altogether.
"No Host Memory" means there isn't enough memory on your server box. Add more physical memory, and/or reduce the number of application running.