I now followed the description of how to remove the captcha, ever since I get ther "parsererror" when logging in and the layout is faulty.

So what can I do? Captcha doesn't work, despite the right PHP settings and all plugins/javascripts disabled...

But when I remove the captcha question from the join form as described here then my whole page is faulty. 

Also clearing all caches, enabling/disabling the Dev-mode has no result...

I am lost

When you open your URL like this: http://yoursitename.com/base/captcha/ do you get any errors?

no, I don't get any errors, I only get a captcha image which is NOT displayed, I mean like a dead link (src) image, the same as the not displayed captcha image on the join form

I am thinking now of removing only the captcha test... but not the captcha from the form... that may help that people can join (though captcha not right) but the form untouched... maybe that will help?

Martin, can you please make sure that all kinds of error reporting are enabled on your server?

even with debug mode... when i open .../base/captcha  I don't get ANY message only the image with the broken link (I mean NO image) ;)

also the join form: no error message even with debug mode

No, I mean error reporting on your server, php error, apache errors any other errors. Because you can't see the error, however it should be there on that page:  http://yoursitename.com/base/captcha/

But its one thing to have captcha not working, its another thing that when i change the join.php and join_index.html EXACTLY as described (and I understand html, CSS and php) that my WHOLE SITE is affected!!!

It happened before, when I changed core files according to description, that I had to replace them again with the originals...

I don't find anything to show me the errors in the browser, but the error log in the cpanel doesn't show any errors as o this morning, only some from last night concerning config.php, that is every moment when I was changing the dev-mode it logged an error.

But for this morning no error logs

very interesting.... I didnt get any error messages in opera or Safari, but now in Firefox I get (in French) the following (my own translation): 

The image "http://jambo-congo.net/base/captcha" cannot be displayed because it contains errors.

By the way: this message comes only in Firefox! Other browsers (Chrome, Opera, Safari and IE) show only a broken link image.

That's what I'm talking about, the error is behind this image, image is displayed instead of errors. which is why we need error reporting of all kinds to be on. 

I checked which plugins i installed since the last new user subscribed: Attachments and Site Tour. Both I disabled but no change.

I cannot change my PHP settings to get error messages. I have in the CPanel only a window "error logs" and they don't show any captcha related error, not even ANY error for this morning.

Contact your provider support team and request to?

sorry, I reloaded the page, this debug message is gone, I see the join form correctly, no error messages.

But judging from the thousands(!) of views of the "captcha gone" sticky topic, Oxwall seems to have too often problems with it :(

Please, how can I just get rid of it - and not messing up my site? I am trying again and again, but the slightest change of a file (join.php, join_index.html) messes everything up

As I noted earlier, please contact your hosting provider support team and request to enable all possible kinds of error reporting on your server. 

My server support no longer answers...

I tried a last time changing join.php and join_index.html which works so far that captcha is no longer required, but it messes up the layout and plugins...

At least I have now a temporary solution:

1. I use Smart Captcha with only one possible answer

2. I changed "Captcha" in all language keys with the question that should be displayed by the captcha image. So the user DOES see the question and is able to answer it, though it will be always the same question... :)

So my site works, joining the site works... but the problem is not solved yet...

My server support (Arvixe) suggested it may be Cloudflare. I asked them to change the name servers again back to the Arvixe name servers. I have not heard yet from them, but when I open jambo-congo.net/base/captcha/ or jambo-congo.net/smartcaptcha/smart-captcha/ I get the code from a PNG file - looking correct.

But the join form does not yet show a captcha image. Maybe it still needs time to propagate the new name server entries.