There are couple errors in asp.net related to viewstate
1. System.Web.HttpException: The client disconnected. ---> System.Web.UI.ViewStateException: Invalid viewstate.
2. System.Web.HttpException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. ---> System.Web.UI.ViewStateException: Invalid viewstate.
How to fix?
1. Check Application Pool Recycling IIS setting
The fix in this case is to adjust the settings on the application pools so that recycling is less likely to occur at peak periods.
2. put machineKey section into your web.config (http://www.aspnetresources.com/tools/keycreator.aspx)
Such as:
<machineKey
validationKey="80FE3D40B4CDD7FBC1DC32FA0DC87C83586B651214A19F4BC140970DEAE7F99A6B24D2323DB2088E472194BF14CB996062B41F9C2D3A4D821091AA53282F55D5"
decryptionKey="DA085C28238653E0C85994B40AB4208236E0E814BF698F9C202A80901C00F613"
validation="SHA1"
decryption="AES"
/>
References:
1. Intermittent Invalid Viewstate Error in ASP.NET Web pages
http://support.microsoft.com/default.aspx?scid=kb;en-us;555353&sd=rss&spid=6351
2.ASP.NET state management: viewstate
http://www.aspnetresources.com/articles/ViewState.aspx#
