Whenever you see this behavior, it is likely one of the following items.
 
  1. This means the AJAX cart module is not written to Magento standards. Its controller file is outputting using “echo” and then not exiting directly after output.
  2. To resolve, go to Extendware -> Manage Extensions -> Overview, click Third Party Extensions to the left and input “Cart” as the name. 
  3. Look at the list and determine which Cart extension you are using.
    1. Note : If the “Identifier” column of the extensions is called "Company_Cart", then you would go the controller files in app/code/local/Company/Cart or app/code/community/Company/Cart and look in “controllers” directory. 
  4. Open up the files and any functions that use “echo” add an exit to the end of the function and it will be resolved.