windows service using CRM sdk gives error The security context token is expired or is not valid

I am running windows service on CRM server which calculate some values from another database and update CRM 2016 on premises custom entity records. I am using earlybound entity class in my windows service. service running and updating records. but i get this error after about 40 mins.

System.ServiceModel.Security.MessageSecurityException: An unsecured or incorrectly secured fault was received from the other party. See the inner FaultException for the fault code and detail. ---> System.ServiceModel.FaultException: The security context token is expired or is not valid. The message was not processed.

What could be the reason for this error ? and how to resolve this. eventhough all the records updated it hangs in the middle of the process.

I always get better answers from the forum so expecting a good one :)

thanks all