When you create a panel, Panels returns an identifying handle in PPB-Panel-ID. Each panel you create is given a unique handle. When working with a specific panel, PPB-Panel-ID must contain the handle that was returned when that panel was created. Failure to specify the correct handle is a common cause of problems when using Panels.
You should not assume that Panels allocates any particular identifier to a particular panel. Neither should you assume that the same identifier is used for two different executions of the same program. Always use the identifier returned by Panels when the panel was created.