At least on Windows 7, Popeye 4.83 (64-bit) crashes with

input-error:

when I include the side-to-move in Forsyth mode, e.g.:

BeginProblem
Forsyth rsbqkbsr/pppppppp/8/8/8/8/PPPPPPPP/RSBQKBSR w

This seems rather harsh even if that component isn't expected, and such notation seemed to be accepted as intended in version 4.69.