If you have above error displayed as soon as you do post back on your page while rest of your app is still working then you might have huge viewstate data in your page.

Normally it happens when you are loading a page displaying several hundreds records, that may generate very big viewstate value inside your page. The loading will work fine but as soon as you post back the page it will throw that error. Reason is your page becomes too bulky to be accepted by server.

To solve the problem you obviously have to reduce the side of the viewstate by either disabling viewstate on your page or disable on selected controls where it is not needed, if both of these is not possible then simply reduce the number of records displayed at a time.

Ok, that’s a generic solution but in Asp.Net framework 2.0 you can handle it by using an in-built feature called “Viewstate chunking”, this will chunk out the viewstate data so that not a single large element is generated.

Update: If you are using framework 1.1 then there is an option of in-memory viewstate compression. Check this link for more details ( I have implemented it using vb.net so you can ask me for help).