After cPanel version 11.42 released with PHP 5.4, the seagull mode needs to be updated to be work stable with PHP 5.4 also.
So, after run update RVsitebuilder to latest version (5.2.13) to support PHP 5.4, some servers need to run update seagullmode also with the following command.

perl /usr/local/cpanel/whostmgr/docroot/cgi/rvsitebuilderinstaller/autoinstaller.cgi --force=rvseagullmod

Then run update RVsitebuilder again.
perl /usr/local/cpanel/whostmgr/docroot/cgi/rvsitebuilderinstaller/autoinstaller.cgi --force=rvsitebuilder

After that, republish the website, the error will be gone.

** Since 2023: cPanel Version 112 released,  the seagull mode needs to be updated to be work stable with PHP 5.6+ also.