C# Excel export does not work only on Chrome browser

Client: Chrome Version 41.0.2272.89 m

ContentType: "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"

Excel export used to work till last Chrome update. It works well on Firefox and IE. When I hit export, a file with no extension downloads. If I manually change extension of this file to .xlsx then it opens in excel. Any help appreciated. Thanks.