Error validating proxy
This message generally means that a memory allocation has failed.
In some types of hang conditions (e.g., all IBM HTTP Server child process/threads tied up waiting for the application server to respond, and the application server isn’t responding because the application processing the request is hung), this “Max Clients” message will be written to the error log.
If the request is not expected, check for links on your site which specify that URL.
If a directory listing was supposed to be returned, enable the Indexes option for that directory.
I.e., all child processes/threads are already in use handling existing requests.
The message is only written once during the life of the server, but the peak condition may happen any number of times after the message is logged.