WordPress throws this error when the function delete_site_transient fails. The function tries to remove a site‑wide transient from the options table or from an external object cache. Failure occurs when the database does not allow the delete operation, when the cache server is unreachable, when the transient does not exist, or when the current user lacks required capability. The error appears as a WP_Error object and is logged if debugging is active.
In multisite environments only a super admin can delete site transients. If a lower role triggers the deletion the function returns false and wraps it in WP_Error. Corrupt option names or an active install flag also cause the function to abort.