First step is learn how to examine the test log, refer to
https://www.ibm.com/support/pages/troubleshooting-playback-errors-rational-ibm-performance-tester-http-tests
If the test is in a schedule with multiple VU's, simplify the issue, just play back the test.
Compare where the test fails with the recorded request. If the message is a failed substitution, then this means there was a failed extraction upstream, so the search changes to find out why the failed extraction happened.
This becomes a debugging exercise.
Chances are if it fails every 2 days there's a cookie, some session ID or something that expires every two days and we're sending a static value instead of a dynamic value and this causes the test to fail.
We call this a data correlation issue. I suggest opening a Salesforce ticket so a support person can look at your test log.
When opening the ticket, highlight the result in the Test Navigator, right mouse click and chose Export..Test...Test Assets with Dependencies.
This makes a .zip file, attach the .zip file to the ticket
Thank you
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