If you are using the CoolURI extension for a Typo3 installation managing several websites with multidomain support, you might run into 404 error problems.
This depends on your individual server configuration.
Internally, cooluri reads the requested domain from the php server array by asking for the server name: $domain = $_SERVER['SERVER_NAME'];.
Often, this does not return the request domain but an internal server name.
To fix this issue you have to edit the cooluri extension file typo3/conf/ext/cooluri/class.tx_cooluri.php
Replace all occurences of $_SERVER['SERVER_NAME'] with $_SERVER['HTTP_HOST'], refresh your typo3 caches and fore cooluri to update all cached urls.
As an alternative, you can use t3lib_div::getIndpEnv('HTTP_HOST') instead of $_SERVER['HTTP_HOST']. In the according cooluri bug report (http://forge.typo3.org/issues/35799) someone recommended this to also support setups with a proxy configured in front of typo3. However, I never tested this up to now.