You may safely ignore this message because it reflects the normal, secure operation of your Magento installation.
If the IP address shown in the log is your site’s IP address, it represents the Magento installation performing a routine security check. Its presence in the error logs indicates that the local.xml file, which contains sensitive credentials, is inaccessible over the Web. Your Magento installation performs this check whenever you log into the administrative control panel of your site.
If the IP address in the log is not your site’s IP address, it reflects a successful block of an external attempt to access this file, and is therefore desirable. The access attempts are sometimes made by automatic site scrapers or bots that search for vulnerable websites.