I have to check, it's been a while since I installed and played pop.
Been on holidays, sorry for the late reply.
The issue with the MyIDE-2 is that the file is loaded from CF to internal memory first, then executed.
Since pop is larger then the internal sram of the myide-2, you get this error message.
You could use SIDE, that I patched for use with MyIDE-2
But I do not know how SIDE itself handles FAT-files.
Since it's patched, it does not know myide-2/sram, so it I guess it loads directly from FAT.
Not sure if the loader is overwritten by loading pop, crashing the system though.
Please give a (newest) link to pop and I have a look, it's weekend anyway
Then I can recommend what flashcartridge you need.
These cartridges can be flashed from out your atari, by loading a flasher-image over SIO.
Grtz,
Sijmen.