registering add-on of edited system form in sap b1 9.0

Hi All,

I have a problem in SAP b1 9.0. 

  Actually I modified the operation of A/R Invoice, so I want to register an add-on of that system form in SAP b1 9.0. 

  When I create file of .ard as we watch it in video of Bryan Gomez 

  Creating and Registering SAP Add-on - YouTube 

  it will be created correctly, But the problem is when I register that the file of .ard it gives error (Cannot create a file when that file already exists). Again when I create a file of .ard . 

  But when I create and register the add-on of TabOrder,AddingMenuItems in Sample folder of SDK it will be registered correctly. 

How can I solve that problem.