Thanks, but the URLs are correct, that wasn’t the problem.
However, I thought the problem might be with the .htaccess file so I played around with that a bit and discovered the solution. In the .htaccess file, there are these 2 lines (among others)…
RewriteBase /addon/
and
RewriteRule . /addon/index.php [L]
and I manually changed them to:
RewriteBase /
and
RewriteRule . /index.php [L]
and that solved the problem! All the links are going where they should now, and I’m not getting the internal server errors anymore.
