Fatal error: Call to undefined function enableSemantics()

Fatal error: Call to undefined function enableSemantics() in ... LocalSettings.php: Something went wrong with the registration or installation, please re-read the instillation instructions. 1

Fatal error: Call to undefined function enableSemantics()

This kind of message appears if the Extension "Validator" extension is still explicitly invoked. To resolve this the following line has to be removed:

require_once "$IP/extensions/Validator/Validator.php";

Fatal: Call to undefined function enableSemantics() …: This kind of message appears for MW ≤ 1.21.x if the Extension Installer extension is included after the call to enableSemantics() (see above). Make sure that the call to include Extension Installer comes first.

References

^ Semantic MediaWiki: User mailing list thread "Problem upgrading MW - enableSemantics fatal error"