The registers on the MX150 are exactly the same as the MX170. The firmware for the MX150 uses 2.0nn but the firmware on the MX170 is 2.3nn. The differences are documented at the front and back of this document
Language_Guide_2.30. That is the reason why Rookie 1 will not load.
The changes are reasonably minor mostly relating to how an array is used, in the old firmware you could not pass an array and so had to pass an address with ? and uses the table function in rookie 1 which is now no longer needed for that purpose.
The 2.0 firmware is not available for the MX170 but I do have a few MX150's left with the old firmware on.
Jim
www.byvac.com