Getting an error like this?

SFDC ERROR - INSERT TASK:INVALID_SESSION_ID: Invalid Session ID found in SessionHeader: Illegal Session. Session not found, missing session key: 00DN00000001xpU!ARkAQHV.1RXn.Nr34RSaEyGaq.yzqctjLmw.lpDKqzwFrVl15eE5bd85y4KfeSJzf.t6Z.2U3nNmbeduA71dEeg.607Tqk2M\n

Don’t worry, you have a valid session ID, but you’ve used it against an incorrect sandbox or Salesforce instance! I.e. You have executed a API login() call against test.salesforce.com and then on your subsequent call you’ve contacted cs5.salesforce.com instead of cs6.salesforce.com.

This change in pod usually occurs after a sandbox refresh (Salesforce often moves sandboxes between pods after a refresh). It can also occur with production instances after a pod split.

The best practice is to check the serverUrl field you receive in the LoginResult response and to use this value as the URL in subsequent calls.