I think this might do it (be sure to back up the file first):
Change this line (line 58 in my version) of the core\components\formit\model\stopforumspam\stopforumspam.class.php file
from
$xml = $this->request($params);
to
$xml = $this->request($params);
if ($xml === true) {
return array();
}
And this line in the same file (around line 85):
$responseXml = $response->toXml();
to this:
if ($response->isError()) {
return true;
}
$responseXml = $response->toXml();
Your changes will be overwritten if you upgrade FormIt, so you might want to back up the corrected file for future use (assuming that this works).