You receive may observe warning event in the InTrust event log:
InTrust Server reported a warning:
Error text: Incoming connection attempt has been failed. Source address: <IPAddress>:port#. Error text: ADC Error: User not found (0x8adc3207).
This can be caused when an Intrust Agent's hand-shake is broken on the InTrust server-side but the InTrust Agent is not aware and continues to try and communicate with the InTrust server in question.
If the InTrust service account has permissions to recover/install Agents then the Agent connection should be recovered automatically.
If the Agent was manually installed due to permissions or firewall the Agent will need to be manually hand-shaked with the InTrust server once again. Review the "DVD\Agent\Manual Agent Install.htm" document included with the InTrust download package for more details related to manual agent registrations.