Configuring Application Pool Queue-Length Limits (IIS 6.0)
Application pool queue-length limits prevent large numbers of requests from queuing up and overloading your server. When application pool queue-length limits are enabled, IIS monitors the number of requests for a designated application pool queue before queuing a new request. If adding the new request to the queue exceeds the queue size, the server rejects the request and sends an uncustomizable 503-error response to the client.
You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /user:Administrative_AccountName "mmc %systemroot%\system32\inetsrv\iis.msc".
To change an application pool queue-length limit using IIS Manager