French character output changes on different systems

I have AutoIT v3.2.2.0 installed at work on an XP system ,and at home
on a Windows 2000 system. Last night I wrote a program that reads some
French text from a file (FileReadLine), substitutes guillemes (French
quote characters), and writes to another file (FileWriteLine).

At home the output looks just like the input, e.g.:

 <VALUE>Le média d'archivage « %s » n'est pas monté. Procéder quand
même? »</VALUE>

 but when I run the same program at work, the output has different
characters, e.g.:

<VALUE>Le média d'archivage « %s » n'est pas monté. Procéder quand
même? »</VALUE>

This is not a problem with the local display. The input files look
fine in both places, and the output files I created at home look fine
on the work PC.

How can I fix this?