what is the version of SEPM? there are fixes in RU6a for PHP issue, though not specific to the Query failed error, however PHP has role in the data fetching
http://www.symantec.com/business/support/index?page=content&id=TECH103087&locale=en_US
Periodic CPU spike when using Symantec Endpoint Protection Manager Java console
Fix ID: 2022713
Symptom: With RU6, a periodic CPU spike occurs when a user selected the Policies, Clients, or Admin page in the Symantec Endpoint Protection Manager Java-based console.
Solution: This issue was caused by a periodic refresh of the Home page to prevent a time-out of the PHP session. The refresh task now refreshes the Reports page, which consumes fewer resources. In addition, you can now configure the refresh time by setting the scm.keepalivescheduleminute value in the conf.properties file.