Unable to validate data, ASP.net error

Error:
Unable to validate data, ASP.net error at System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)

Information:
This is an View state decoding error.

Cause:
The basic reason of this is the difference of key while encrypting and decrypting the viewstate data. Suppose an asp.net rendered a page with key1 and saved the page state in view state, meanwhile asp.net’s key is changed to key2, now when some server side event will occur on page the viewstate will get decrypted and this error will occur as the old view state is now not valid due to a different encryption key.

It may occur when you open a page for along time and after that do some events on that.

Solution
Fix the key in your web.config file, so that only one key is used to encrypt and decrypt the viewstate data.

For more information visit:

http://www.experts-exchange.com/Programming/Programming_Languages/Dot_Net/ASP_DOT_NET/Q_21321364.html

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q312906