I think you are facing this problem because of ViewState
. ViewState
is only retrieve the data for the same page.
If you navigate to some other page then that value becomes null on the page load event.
So, instead of ViewState
you can use SESSION STATE
variable.
SESSION
is also use to store the data but advantage in this is, you will get the data even after navigation of the page.
I hope you this will solve your problem.!