Error after upgrade

If anybody can confirm is this a known issue or I have done something wrong.

There’s something wrong with your installation. Try running the server scanner to identify the problem: https://s2member.com/kb-article/server-scanner/

I have only 2 warnings with server-scanner, but i think that has nothing to do with my problem.

The error I am receiving on browser console:
Failed to load resource: the server responded with a status of 500 (Internal Server Error)
https://mywebsite.com/wp-content/plugins/s2member/s2member-o.php?ws_plugin__s2member_css=1&qcABC=1&ver=151218-3402031376

Server-Scanner output:
Notice[NOTICE] WordPress Memory Limit:
Although NOT required, s2Member recommends that you raise your WordPress memory limit (please set: WP_MEMORY_LIMIT in /wp-config.php), to at least 64M (i.e. 64 megabytes). Please see: this how-to article. Or consult with your web hosting company about this message. Your current memory limit allows only: 40M

Notice[NOTICE] WordPress DB Charset:
Although NOT required, s2Member recommends that your WordPress installation be configured to operate with a UTF-8 database charset (please set: DB_CHARSET in /wp-config.php). Please see this article for further details. Or consult with your web hosting company about this message. Your current DB charset is set to: utf8mb4

I’ve just deleted the plugin, deleted all files from plugin folder, reinstall it, but again I am getting same error.

I had similar problem

The problem for me was caused by iThemes Security, which I know a lot of you may use

In the iThemes Security Settings page > System Tweaks, uncheck the box marked “Filter Long URL Strings”

Phil ??