The stream handler is required to support this message because SpiGetHandler uses this message to install the default SPCB in the stream handler. The stream handler must support the installation and removal of SPCBs, but not the replacement of an SPCB. The stream handler fails an install if the SPCB exists. The Sync/Stream Manager fails any installation or removal of SPCBs with ulIntKey equal to 0. This prevents one process from affecting the stream creation of another process.