Hi Vij,
Since it's a Z application, you cannot use AET for this rapid application.
Instead of trying to add a new field , If possible delete the rapid application which you developed and confirm the fields of the table first and then create the application.
Even if you are successful in adding a new field, you may always trigger with new errors.
For further details go to the package which you have used via SE80 for any Logical changes
Thanks & regards
Sharad