In this situation the USM-810 and USP-2 versions 1.001 or earlier are connected on the same loop of an IQ System Interface (INT2 or INT3). This was a firmware glitch and the problem will not occur if the USM-810 is on a separate
Resolution: USP-2 firmware 1.002 or later is needed for same loop operation of a USM-810 and USP-2 modules on an IQ System Interface. Firmware chips can be obtained for the USP-2 from the Crown Parts Department and the USM-810 firmware is available for download from the Crown Web Site.