can any why this error has occured

Hi [mention:c85d80fec22e458daf0645f291934c2f:e9ed411860ed4f2ba0265705b8793d05],

I suggest you paste the code that is triggering this error in order for the Community to be able to help. 

I suggest you look at the Appian logs (the stdOut is the place to go to). One common error is where a datetime field has an invalid value in it (e.g. a datetime might contain '0000-00-00 00:00'), but the logs will give you the definitive error.