The error message I got was:
Fatal error: Cannot redeclare add_screen_meta_link() (previously declared in /home/content/16/6136616/html/wp-content/plugins/broken-link-checker/includes/screen-meta-links.php:256) in /home/content/16/6136616/html/wp-content/plugins/gantry/admin/screen-meta-links.php on line 205
I moved the endif; to just before ?> as you recommended, and it still didn't help, so I simply removed the last function in the screen-meta-links.php file. Anticosti didn't say which function he had to remove but I saw that, in the original file, after the endif; there was one whole function. I deleted that and my problem went away. If it continues to work, I may just live with that but if there is a fix I'd like to know.
I've been working on this site, using the Gantry-based theme, since early May. I never saw that error until I tried to activate the Broken Link Checker to check something: I had changed the name of a page and wanted to see if there were any links to it that I'd missed.