It is likely that the issue could be resolved with reconfiguring your Apache configuration file (/etc/httpd/conf/httpd.conf). The problem may be that you have run out of available Apache processes.
To determine if your VPS's Apache web server has reached its MaxClients settings search the /var/log/httpd/error_log for a line similar to:
[Mon Apr 10 11:16:49 2006] [error] server reached MaxClients setting, consider raising the MaxClients setting
The default Apache configuration file settings relating to MaxClients are:
MaxClients limits the number of simultaneous requests that can be supported. In the default case, ten requests will be served; any additional requests will be rejected. In times of high traffic volume this will appear as the web server being down to any requests past ten at that moment.
If your site receives relatively high traffic, we recommend that you change the following settings in your Apache configuration file (/etc/httpd/conf/httpd.conf) then restart the Apache service:
Replace <N> with an appropriate number of processes. You will need to set this number between 10 and the (maximum number of processes your VPS will support) - (processes needed for other services on your VPS). We recommend not raising MaxClients by any more than and additional 50. For Example, to change the MaxClients value to 60 change:
To make these new settings take effect you will need to restart your Apache web server. Test the new settings and determine if you need to raise MaxClients further.
You can find more information these Apache configuration directives at the Apache website at http://httpd.apache.org/docs-2.0/mod/quickreference.html.
If the above fails to solve your problem, email email@example.com for an alternate solution.