Occasionnally, I get this message from an .ASPX page:

"Unable to validate data"

This is the stack trace:

at System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32& dataLength)
   at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)

This is an error which seems to happen at the .NET level as I cannot trap it in my application. Anyone would know what could be related to that?