Hello,
on my website contact seller is posible only to registered users. When I try to send a message to other seller, the name and e-mail is autocompleted and there is no way to change this field. After I wrote a message and clicked send there is an error:
"Your name: this field is required
Invalid email address"
Any sugestions?

URL: http://testowastronaogrywania.cba.pl/

I am not sure if osclass has option to allow only logged to contact seller. I will check issue with required message.

Listing -> Setting -> Contact publisher: Only allow registered users to contact publisher. This is basic function in osclass...

@pavels
In file:
oc-content/themes/zara/item-send-friend.php

change code:
        $('#yourName').attr('disabled', true).addClass('disabled');
        $('#yourEmail').attr('disabled', true).addClass('disabled');
to:
        $('#yourName').attr('readonly', true).addClass('disabled');
        $('#yourEmail').attr('readonly', true).addClass('disabled');

@frosticek
Thanks. It works now.

I have another question... After send a e-mail to seller (in small window), the message "We`ve just sent an e-mail to the seller" is showing in the same small window... Is it possible to close the small window and show the message "We`ve just sent...." in the main window?

@pavels
In item-send-friend.php (theme folder) and item-contact-seller make sure all forms (<form>) has attribute:
target="_top"
That will make content load in original window, not in fancybox.

Thank you. Problem solved.