Emon51 is a monitor from Elektor.

They don't use Intel Hex for downloading but a hexfile which is created by their assembler
This format differs sligtly form INTEL Hex (no : at start of line for example)

So you should either convert your hexfiles to that format or change the monitor. Elektor provides source for the mon.

As far as I can remember (emon51 is from
early 1990) there is a modified version emon52 which supports intel hex.

emon51 was designed for Elektors Compuboard and I am not shure if it will work with other HW.

If you need more infos on this format please send a email to me and I will try to search my backups for more info.

Thomas