I have a form that contains the functionality of uploading multiple excelsheets(office 2007 with extension .xlsx)  that contains purchaseorder data.

It was working fine for uploading a excel sheet with file upload control in dotnet. As I need to upload multiple excelsheets I have used ajax uploader in place of fileupload control. It is working fine in uploading multiple excel sheets if the extension is .xls but it is giving problem if the excel sheets contain the extension of .xlsx.