Failed saving comment is the message that appears when we fail to save the comment (LOL)
$database->SetQuery("
INSERT INTO jos_comment
(contentid,component,ip,userid,usertype,date,name,email,website,notify,title,comment,published,voting_yes,voting_no,parentid)
VALUES(
'$this->_content_id',
'$com',
'$ip',
'$userid',
'',
'$datenow',
'$name',
'$email',
'$website',
'$notify',
'$title',
'$comment',
'$published',
'0',
'0',
'$parent_id'
)");
$result=$database->Query() or die(_JOOMLACOMMENT_SAVINGFAILED);
Would you check if you have the jos_comment table and if it has the following fields:
contentid,component,ip,userid,usertype,date,name,email,website,notify,title,
comment,published,voting_yes,voting_no,parentid
