Regentronique Links Checker - Error 404

[exdiogene]

If you look at the .htaccess content in the first post you will see a section containing at the beginning "# MyBB "search engine friendly" URL rewrites" and at the end "SetEnv SEO_SUPPORT 1".

So this show that at some point you used that SEO plugin but forgot to replace the previous .htaccess file afterward.

If you just replace this file, the Links Checker should work without any issues.