Paid Memberships Pro + Theme my login + Gravity Forms (with User Registration)

Hi, I am using paid membership pro, theme my login and Gravity Forms with “User registration” add-on.

My subscription form are created with Gravity Forms. My users can subscribe with no problem but when they want to login (the login page just contain the theme my login shortcode), they arrive on a error 500 page (but if they refresh the error 500 page they finally arrive on the good page).

Below the error i found in my error log files (the first line is when the user created is account), next lines are when he try to login :

[13-Oct-2017 09:31:10 UTC] PHP Warning: Creating default object from empty value in /home/rciziapqb/public_html/wp-content/plugins/pmpro-register-helper/pmpro-register-helper.php on line 578
[13-Oct-2017 09:39:58 UTC] PHP Warning: Illegal string offset ‘last’ in /home/rciziapqb/public_html/wp-content/plugins/paid-memberships-pro/adminpages/reports/login.php on line 402
[13-Oct-2017 09:39:58 UTC] PHP Warning: Illegal string offset ‘alltime’ in /home/rciziapqb/public_html/wp-content/plugins/paid-memberships-pro/adminpages/reports/login.php on line 403
[13-Oct-2017 09:39:58 UTC] PHP Fatal error: Uncaught Error: Cannot increment/decrement overloaded objects nor string offsets in /home/rciziapqb/public_html/wp-content/plugins/paid-memberships-pro/adminpages/reports/login.php:403
Stack trace:
#0 /home/rciziapqb/public_html/wp-includes/class-wp-hook.php(300): pmpro_report_login_wp_login(‘jonathan005’)
#1 /home/rciziapqb/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(NULL, Array)
#2 /home/rciziapqb/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#3 /home/rciziapqb/public_html/wp-includes/user.php(104): do_action(‘wp_login’, ‘jonathan005’, Object(WP_User))
#4 /home/rciziapqb/public_html/wp-content/plugins/theme-my-login/includes/class-theme-my-login.php(482): wp_signon(Array, true)
#5 /home/rciziapqb/public_html/wp-includes/class-wp-hook.php(298): Theme_My_Login->template_redirect(”)
#6 /home/rciziapqb/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(NULL, Array)
#7 /home/rciziapqb/public_html/wp-includes/plugin.php(453): WP_Hook->do_action( in /home/rciziapqb/public_html/wp-content/plugins/paid-memberships-pro/adminpages/reports/login.php on line 403

Did you know what can be the error ?

Thanks by advance