Hi Guylain!

>
> So, what is the correct way to get arround that problem?
>
> Should I upgrate my ICU dll's on my Windows box to version 4.4? Is it possible to do that anyway?
>

That won't be possible AFAIK and wouldn't help either.

> Or is there a way my customer downgrade to version 3.0?
>

Yes. The problem is that firebird is broken with ICU 4.2+. Debian's ICU
support for firebird is broken too because of this. The only option
would be to do a manual install of firebird (not via Debian's apt-get).
The binary kits usually contain a compatible version of ICU which is
specific to that firebird version. After removing the original Debian
packages you wanna start here:
http://www.firebirdsql.org/en/server-packages/

Maybe somebody has build some unofficial .deb Packages which fix the
issue. But i don't know for sure.

hth,
Michael