Biztalk: Instance was not successfully terminated. Status is Pending
Sometimes when you try to terminate messages in Biztalk, messages may fail to terminate. Before you force the termination, you need to make sure you are ONLY terminating the messages you intend to terminate.
To force the termination, try one of the following:
Restart/Stop host instances assigned to the port or orchestration
Recycle the application pool assigned to the Webservice/WCF service if the port’s host is an isolated host
You can also wait for Biztalk to finish retrying sending the message, hence messages become suspended instances