Two days later and a lot of online research!! this issue has been logged as a ticket with Autel as rather urgent and still no reply, never the less the problem has been temporarily resolved. When I received the MD802 in January this year a backup copy of the SD card was made of the original software (version: V4.40) before proceeding to do the latest software upgrade to (version: V4.50) it was this version of software that rendered the unit in capable of communicating with the Nissan Hard Body ECU, the new version (V4.50) was deleted from the SD card and the original version (V4.40) was copied back onto the SD card, hey presto the MD802 is now able to communicate with the ECU. This was a short lived sense of accomplishment, now being able to communicate with the ECU and retrieve the DTC's the codes returned are as follows.