...
$wgReadOnly = 'Upgrading to MediaWiki 1.16.2'; In the localsettings.php file.
However, it doesn't stop me editing pages (I was hoping it would make the entire wiki read only !)
Any ideas why ?
Perhaps you edited the wrong file?
Perhaps you added it before the include of DefaultSettings.php?
Perhaps you misspelled wgReadOnly?
Perhaps you have it redefined as null later in the file?