* Failure to secure debt deal could undermine asset sale -sources. : DUBAI (Reuters) - A Kuwaiti creditor is refusing to agree to a debt settlement deal with Abraaj, which could push the private equity firm to seek provisional liquidation, three sources close to the matter said. The refusal by Kuwait’s Public Institution for Social Security (PIFSS) to join other creditors in a debt freeze may complicate Abraaj’s efforts to sell its investment management unit to New York-based Cerberus Capital Management, the sources told Reuters.