OK, so it’s the contact button at the bottom of the page? I thought you were talking about that first popup subscription form but that’s in colorbox. Tip: try to limit the number of lightbox scripts on your site to one and use that one for all.
Anyway, I tried the contact form from the bottom button and notice that when I make it fail (by not filling out an email address) there is a div with text appended to the form. It shows the failure notice with a yellow border as it should:
<div class="wpcf7-response-output wpcf7-display-none wpcf7-validation-errors" style="display: block;" role="alert">Fehler beim Ausfüllen des Formulars! Bitte überprüfen Sie Ihre Eingaben und versuchen es erneut.</div>
Notice the class “wpcf7-validation-errors”.
But when the form is sent correctly, the following div is dynamically appended which does not contain any text message:
<div class="wpcf7-response-output wpcf7-display-none wpcf7-mail-sent-ok" style="display: none;"></div>
This time notice the class “wpcf7-mail-sent-ok”.
It might be that there is no text message because there is no german translation for the usual “Your message was sent succesfully” (or whatever) but it does look like that style="display: none;"
is going te be a problem even if there IS a visible message.
In any case, it looks to me like it is unrelated to the lightbox.
You might want to test the form without the lightbox first. After you’ve got it working, you can then wrap it in a hidden div again and open it in the lightbox with a button click.