Thanks.
I also use 12MHz clock and i can see in the IDE menu options 'Arduino Board Configuration" (by selecting Atmega1284 lower left corner) that there is a Clock drop down for 12Mhz. The same dropdown menu has “NO” options for bootloader. By selecting both of these i still get the same error.
In addition to the above selections do i also need to modify the “Migthycore1284.json” since it has 16Mhz or any other files?