Hi Nagarajan
Please check 'doc' directory in the CCO installation directory (probably C:\SapCustomerCheckout_1.0\doc'). Take a look at integration guide. If you haven't done it before set up CCO monitor. If you have access to monitor check the receipts - most likely you can see that some of them have status other than 'Confirmed' (sorry I have it in Polish so I'm not quite sure what is the name of the status in English). If you click on the receipt number in the bottom of the page you'll see the error description.
Also it is a good idea to check logs in the console window as Stephan suggested. And there is a log file in 'C:\SapCustomerCheckout_1.0\log'.
Kind regards,
Radek