SharePoint 2013 package issue

Hi Everybody,

Recently i did normal aspx pages migrate into SharePoint 2013 package. Same code i just copied from noraml aspx application into SP 2013 Package but after migrating some applications are won't work properly. That means after post back my package session data is expire with in fraction of seconds. For ex i have a dropdown i bind some information into that. On dropdown selectedIndex changed event i do some stuff that part of code will work on normal aspx page but after migrating into package 2013 if i select dropdown items then dropdown becomes nothing not only dropdown total page will become collapse. May i know the reason why it happens like this not only one page we have around 150 pages in that package. All the applications are getting one type of issues after migrating, one more thing this will not happen all times some times this will work properly sometimes only we get this problem. I check with my lead and my manager they said there might be some setting issues we might be check with MicroSoft person like that they said. If any one face this type of issues then please share your views out of this issue.