Click on submit button nothing happens

Suddenly a form stops working. Click on submit button, nothing happens.
I cannot generate di debugger code to post here.
No error console or javascript conflicts.
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Chronoforms v 6.1.4
PHP 7.3.14
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What's wrong?

Hi crealiagroup,
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I've no idea - there's not enough information here to know.
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Please post a link to the form - that might give us a clue.
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Bob

Hi Bob, thanks for reply.
Here it is:

This is private content

Hi crealiagroup,
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I can see the problem but not what is causing it. I checked on a stripped down page using a URL like this domain_name.com/index.php?option=com_chronoforms6&chronoform=form-name&tmpl=component but still see the same problem :-(
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You might PM Healyhatman and see if he has any suggestions as he is more familiar with CFv6 than I am.
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Bob

Thanks Bob!

It seems to be trying to get some image select2.png and returning an entire 404 error page instead in the response, have a look at that for me.