Thank you for the help, @Nintendofan885.

I've search the source code for the frase externallinks_user WHERE user_link_id IN which appears in the error message. I found it in the function loadLogUsers of the file pagefunctions.php,

I've noticed that the error message only shows when the requested url is not yet in the log file. That is the error disappears if you have changed the url-status from live to dead. The log file is shown at the bottom of the page. It is always empty when the error appears. Maybe this information can help to solve the problem.