PRINT AT 23,0 and FOR NEXT Loop not working after Fastcall

[boriel]

Unfortunately, I don't know what could be happening.
Usually, if you get an error with FastCall in an ASM routine, it means that you're not returning well.
You need to preserve the IX register upon return (check if any of your routines modifies it).
I would need to have a look at the subroutine(s) using fastcall.