Getting error as Invalid length for base 64 array

Question

Hi,

 

Below is the stack trace:

message: 'An unhandled exception occurred.'
-------------------------- Stack Trace -------------------------------
System.FormatException: Invalid length for a Base-64 char array.
   at System.Convert.FromBase64String(String s)
   at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)
   at System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState)
   at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState)
   at System.Web.UI.HiddenFieldPageStatePersister.Load()
-------------------------End Stack Trace -----------------------------