Rewrite wp-login.php issue after update

Hi,
One year ago I set up a site using the hide wp-login.php feature of the ithemes security plugin. And it worked fine until last week.
I just updated the plugin to version 6. Now I reach the login page, but after filling in the data, I cannot enter the dashboard. I just get a 500 error massage. May you help me fixing this problem.
Best,
Philipp