Very recently I have made some changes on my application after uploaded it to the server I have found this error:
Unable to validate data at System.Web.Configuration.MachineKey.GetDecodedData(Byte buf, Byte modifier,
Int32 start, Int32 length, Int32& dataLength) at System.Web.UI.LosFormatter.Deserialize(String input) e
After doing some r&d got the answer. Hopefully this will helpful for you.