Ok, this seems like a "captcha" related problem.

A long shot, still do you know if you are on a LiteSpeed web server ?

Also this:

http: // www . zzzzzzz . nl/index.php/community/

is WRONG (everywhere in your wordpress urls). Fix it. In permalinks of WP.

Ok, i see that you are on a Windows IIS server. Sorry i have no idea about Microsoft IIS.

(still you should remove the "index.php" from your permalinks)

The only thing the Debug says is:

WordPress Email sending function wp_mail() doesn't work!

Thanks Anonymous20 for your input. Due to the urgency i restored a backup and it seems ok for now.

Posted by: @anonymous20

Also this:

http: // www . zzzzzzz . nl/index.php/community/

is WRONG (everywhere in your wordpress urls). Fix it. In permalinks of WP.

I tried this but that broke my site completely :o.  I think due my inexperience.