Thread:Project:Support desk/several wikis stopped working spontaneously/reply (6)

The second error (unexpected $end, yadda yadda) sounds like when you added that line to LocalSettings.php, you forgot a semi-colon (or removed the closing  of a comment, or some other syntax error was made).

The first error (Mediawiki Internal Error) is really hard to debug without the $wgShowExceptionDetails = true; However, it is unlikely to be caused by lack of html tidy (Which fixes html errors) or stuff wrong in a .htaccess file (which gives a different type of error message - typically an apache generated 500)