My bet is that your Windows programming language is causing the above problem, as it translates the "/" as the Y with the two horizontal lines. It's no wonder the install fails as it needs to read those marks to find the translation for the above strings.
Any idea how I can/should deal with it?
Edit: This hasn't happened when I've installed mods before like aTweaks, Unfinished Business and BG2 Tweak Pack. I don't know why this one would be any different.
What OS do you using Chinese Windows?
64-bit Windows 7 Ultimate.