nextcloud/apps/files_encryption/files/error.php

<?php
if (!isset($_)) { //also provide standalone error page
	require_once '../../../lib/base.php';

	$l = OC_L10N::get('files_encryption');

	$errorMsg = $l->t('Your private key is not valid! Maybe your password was changed from outside. You can update your private key password in your personal settings to regain access to your files');

	if(isset($_GET['p']) && $_GET['p'] === '1') {
		header('HTTP/1.0 404 ' . $errorMsg);
	}

	// check if ajax request
	if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
		\OCP\JSON::error(array('data' => array('message' => $errorMsg)));
	} else {
		header('HTTP/1.0 404 ' . $errorMsg);
		$tmpl = new OC_Template('files_encryption', 'invalid_private_key', 'guest');
		$tmpl->printPage();
	}

	exit;
}
?>