The best way to stop further processing is a "Return" statement, provided you have not yet processed a "Screen" command in the InputScript.

In the case that you describe you need to process a VBScript before knowing that no grid rows have been selected. You need to write a temporary file in the VBScript that you read in the InputScript. For details please see example 9 in

http://www.synactive.com/docu_e/guiscripting.html