Download your WordPress version again, and upload wp-includes/plugin.php of the downloaded WordPress to your FTP.
But I recommend you update to last version of WordPress, if your theme isn’t support you can edit in secundary host.
Try to go to Permanen links options and Save changes, without any change.
Try to import users tables from your old site to the new site.
EDIT: I talk about DB.
It works very well. http://airsoftsharkteam.fr/profil/Edy/
You also need to update your WordPress, last version is 4.1 and you use 3.7.
Your PHP version is 5.3.10, maybe it’ll work if you update your PHP version, contact with your host. (:
This web use 5.4.30 version of PHP.
Use this:
[userpro template=memberlist turn_off_initial_results=1]
(: