I finally was able to fix using hack issue between WP-SC and Mailchimp with famous message "Cheating huh?"
case 'mc_submit_signup_form':
// Validate nonceif (!wp_verify_nonce($_POST['_mc_submit_signup_form_nonce'], 'mc_submit_signup_form')) {
wp_die('Cheatin’ huh?');
}// Attempt the signup
mailchimpSF_signup_submit();
If i disable lines with wp_verify_nonce i can use MC and WP-SC with file cache over .htaccess
Mine question is - what can be an drawback here? I know what is nonce and risk to spammers to abuse this. But if i compare this to previous "cheatin huh?" message this is acceptable.