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Support Article

Tracer Session Error: Session B021.... does not exist



When tracing an agent, the Tracer window opens and tracing is performed for a few seconds. The tracing stops abruptly and an error message displays in a popup window.

Error Messages

Tracer Session Error: Session B021.... does not exist - Please restart Tracer.

Steps to Reproduce

  1. Navigate to Agent management.
  2. Select an agent. 
  3. When the agent starts running, select the agent and click the Tracer. Tracer window opens, but does not trace the agent completely.

Root Cause

This behavior is as per Pega product design.


Here’s the explanation for the reported behavior:

When agents are run, they execute an activity and return to the sleep mode. In the sleep mode, the requestor, which the agents use for the execution, is destroyed since it is no longer in use.

Hence, when the Tracer is used on an agent from the System Management Application (SMA), the trace results display for a single execution. Since the requestor is destroyed immediately after this, the Tracer does not have a session to connect to. Therefore, it reports a disconnection.
However, on clicking each trace line, details such as page data and step information display.

When the agent runs on a new requestor, the requestor dies when the agent run is complete. Hence, the tracer session is unavailable for that Tracer. The Tracer displays a popup when any requestor, that is traced, dies.


Published October 20, 2018 - Updated October 8, 2020

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