Coca-Cola Warns on Profit, Shares Fall  CHICAGO (Reuters) - Coca-Cola Co. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=KO.N target=/stocks/quickinfo/fullquote"&gt;KO.N&lt;/A&gt;, amid signs that  is it losing market share to arch rival Pepsi, on Wednesday  warned that profit would lag Wall Street expectations for the  rest of the year because of weakness in key markets and said  there was no quick fix for its problems.