Blockbuster Posts Big Loss, COO Resigns  CHICAGO (Reuters) - Blockbuster Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=BBI.N target=/stocks/quickinfo/fullquote"&gt;BBI.N&lt;/A&gt; on Wednesday  posted a quarterly operating profit well below analysts'  estimates even before \$1.5 billion in one-time charges, as it  faced falling movie rental demand and higher costs to counter  competition.