POSReady 2009 was, as the name implies, released in 2009, at that time I did not have a cash machine or cash register system where processors were still installed where no SSE could handle. It must also be seen from the side that needs to be to test the updates kept a corresponding hardware. MS does not have to pay attention to the updates for Windows XP Embedded or POSReady 2009 on hardware before 2009, so it is to be assumed that future updates, which we also use for Windows XP, will cause problems for older hardware. For me a more factual explanation for your problem with KB4343674 on your PIII.