Grabber corrupting data during save process


I'm encountering problems with "grabber" tool. (The tool being installed in allegro\tools\grabber.exe)

I'm trying to run a very old Allegro program I made.
I was using ".dat" files made with grabber and Allegro 3.12.
The game is running fine with DosBOX.
However I would like to change 2 files in the dat file.
So I'm using grabber again.
The problem is that after having saved the dat file, the game is not running anymore.

After having spent hours to try to figure out what is wrong with the new files, it seems that the new grabbed files are not the cause of the problem: Indeed, even if I load the original dat file, and save it without doing any modification, the game does not run either.

How is it possible? What can I do to troubleshoot my dat file?
It doesnot matter if some files are wrong or downgraded if I managed to make the program run.

Thank you in advance for your help

[Edit] I'm doing more tests... It seems that as long as the DAT file does not contain FONT files, the load/save without doing modification is OK. The game still runs.
However, if the modified DAT has FONT (*.fnt or *.pcx) the load_datafile("xxxxx.dat") is returning NULL.
My fonts are marked as 'color font' but I don't know if it does matter.

[Edit2] Still searching but can't find any mistake... Is that the correct forum to post this question?

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