Network Programming in .NET

Everybody who has worked with ASP.NET will be aware of the page viewstate. .NET’s way of persisting session information using hidden values on the page. However, you may find that if you accidentally post a viewstate from one page to another, or for some reason the worker process looses track of the page viewstate (such as within a server farm, or, as I suspect, where multiple worker processes are handling the same client) – you get an error such as the following:

 

[HttpException (0x80004005): Unable to validate data.]
   System.Web.Configuration.MachineKey.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) +195
   System.Web.UI.LosFormatter.Deserialize(String input) +60

[HttpException (0x80004005): Authentication of viewstate failed.  1) If this is a cluster, edit <machineKey> configuration so all servers use the same validationKey and validation algorithm.  AutoGenerate cannot be used in a cluster.  2) Viewstate can only be posted back to the same page.  3) The viewstate for this page might be corrupted.]
   System.Web.UI.LosFormatter.Deserialize(String input) +118
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +101

[HttpException (0x80004005): Invalid_Viewstate

 

You can of course, use persistant storage, such as SQL server to store the viewstate, but if it is just a rare occurance, you can have the page handle the event gracefully as follows

 

 

That is, if the viewstate’s bad. then reload the page without any post data.

 

You can also return null from this procedure without redirecting, but this may have some unusual side effects.