Hi Ashwani,
First would you please define your steps how you proceed for the generation of stack.xml file.If possible please follow steps from link as mentioned below:
http://basisdomain.wordpress.com/2013/04/04/stack-generation-in-solution-manager/
How to Create Stack.xml file Screens Step by Step - SAP BASIS ANSWERS | SAP BASIS ADMIN BLOG
Hope this will help you.
Regards,
Gaurav