Blockbuster continued the fight of its life Monday, even as stocks in the company slid once again following a report by company auditors PricewaterhouseCoopers expressing substantial doubt that the video-rental outfit will be able to continue to fund its operations. Meanwhile Standard & Poors lowered Blockbuster's debt rating to "CCC" from "B-." The new rating suggests that the company is "vulnerable to nonpayment" of its obligations.