Failed to load viewstate. The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request

Hi,

We have a website developed in .net framework 3.0. It's working fine. It uses view state extensively.
In each and every page there is a grid view. We can edit, save and delete records within the gridview.
We have migrated the same website to .net framework 4.0. I was able to edit and save. After once the save operation is done, if i click on any control on the grid view. It's throwing the below error.
"Failed to load viewstate. The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request".
We haven't done any thing new in this website just migrated it from 3.0 to 4.5. We cann't make view state as false as this website uses view sate extensively. 

Can any provide help on this.
Thanks in advance.