i've the same problem, only if i use the captcha field, in chrome and iexplorer.
so with the captcha fields, if i leave all the fields blanks and i click on submit it seems that the form start to send the email, but i can't see any error messagge (all the fields are compulsory) and there ise the infinite circular arrows.
i noticed that the form has the same behaviour if i fill all the field icluded the captcha.
if i remove the definition of the input field (response field):
[captchar captcha-686 4/4]
and i click on submit i recevive the error message "There was an error while sending your message. Please try again later or contact in another way the site administrator."
so maybe the problem is in the validation function??
here is the definition of the form:
<p>Il tuo nome (richiesto)
[text* your-name] </p>
<p>La tua email (richiesto)
[email* your-email] </p>
[text* your-subject] </p>
<p>Il tuo messaggio
[textarea* your-message] </p>
<p> Inserisci il codice di verifica:
[captchac captcha-686 size:m] [captchar captcha-686 4/4]</p>