Tobias Battenberg

@Berry: Ok, this seems to be different to my problems! Maybe there is a conflict with your jQuery version. Maybe you can try to use a lower version of jQuery? But this is only an idea … please share your solution if the plugin-developer helped you successfully!

I fixed it by myself … in wpmd-login-form.php i changed the following:

From:
if (!res.match(/success/)) {

To:
if (!res['success'] == true) {

Old:

success: function (res) {
    if (!res.match(/success/)) {
        $('form .alert-danger').hide();
        $('#loginform').prepend("<div class='alert alert-danger' data-title='<?php _e('ERROR!','download-manager');?>'><?php _e('Login failed! Please re-check login info.','download-manager');?></div>");
        $('#loginform-submit').html(llbl);
    } else {
        location.href = "<?php echo esc_attr(esc_url($log_redirect)); ?>";
    }
}

New:

success: function(res) {
    if (!res['success'] == true) {
        $('form .alert-danger').hide();
        $('#loginform').prepend("<div class='alert alert-danger' data-title='<?php _e('ERROR!','download-manager');?>'><?php _e('Login failed! Please re-check login info.','download-manager');?></div>");
        $('#loginform-submit').html(llbl);
    } else {
        location.href = "<?php echo esc_attr(esc_url($log_redirect)); ?>";
    }
    
  }

But you have to know, that i use this file from an old version cause i have copied it into my theme-directory to customise the form.
But now it works …