After repeatedly maintaining that it was in no danger of going under, Blockbuster on Monday warned that if it is unable to complete loan deals, it may be unable "to continue as a going concern." Blockbuster, the largest movie rental company, has faced daunting challenges from kiosk operators, online rental outfits (particularly Netflix), and pirates. Although the company said last week that it had received a $250-million revolving loan maturing in 18 months, it indicated on Monday that the loan was subject to certain conditions that it might not be able to meet and that while it expected to close the deal with the lenders by about May 11, "there can be no assurance regarding these matters." The statement, made after the markets closed on Monday, sent shares of Blockbuster tumbling more than 10 percent in early trading today (Tuesday).