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Home > Success Center > Web Performance Monitor (WPM) > Error: Unable to cast object of type 'System.DBNull' to type 'System.String'

Error: Unable to cast object of type 'System.DBNull' to type 'System.String'

Created by Tiarnan Stacke, last modified by MindTouch on Jun 23, 2016

Views: 145 Votes: 1 Revisions: 4


This article provides brief information and steps to resolve the following error when adding transactions to a player:

Unable to cast object of type 'System.DBNull' to type 'System.String'


WPM version 2.0 or later


The issue is caused by an Orion Migration to a new Server with a new Hostname/IP Address.

This causes a new entry to be created in the Engines table but it doesn't update the WPM Agents table with the new Engine ID.



  1. Open Database Manager.
  2. Right-click the Orion Database, and then select New Query.
  3. Paste the following in:
    SELECT *
    FROM Engines

You can use Engine_old if it is available. ticket 951266

  1. Take note of the EngineID of your Polling Engine.
  2. Now run the following query (Please note this will update the WPM Agents to all talk to the Primary).

    UPDATE SEUM_Agents
    SET PollingEngineID = '5'

  3. If you have WPM Player which also talks to Additional Polling Engines then do the following:
    SELECT *

    FROM SEUM_Agent

  4. Enable Table Editing.

  5. Change the Pollingengineid of the Agents which talk to Additional Polling Engines.




Last modified
05:15, 23 Jun 2016