Element was found by backup search only!

This means that your find logic is not absolutely correct. Test Studio is able to locate the right element by a backup search not by the primary find logic.

It seems you are using an older version since it's disabled by default in the latest version. In order to disable the backup search in the current version you are using go to step properties and set the UseBackupSearch property to false, as shown in the screenshot provided. Now your test will fail with "Element not found" exception. So you need to change the find logic.

In older versions if the element is not found by the primary find expression, you will get the following message in the log, but the test will PASS:

"Element was found by backup search only! We recommend editing the element to correct the primary find expression."

In 2012.2.1204.0 if the element is not found by the primary find expression, you will get the same message in the log, but the test will FAIL.

I am sorry but you cannot turn on the backup search.

We took a long hard look and concluded it was causing more harm than good. As a result we have made a firm decision it will never come back. It's important to create/update tests to work properly despite dynamically created html pages.  

Please don't hesitate if you have additional questions.