Problem maybe solved... weird though.
It seems that I've solved this issue. But I don't understand how it works. So please, if anybody of you can come up with any guess, please don't hesitate to share!!!
It happened like this. I ran the compiled exe files on my pendrive in different directories, and I found that at a location it work, while it didn't work at the other one. I began filtering the system files (and abandoned the guess that XLSReadWrite does cause any trouble), and found that once I removed vcl50.bpl, and left vclx50.bpl in the directory of the exe, it worked! But as soon as I copied it back, it gave the initialization error.
Now how weird is that? I'll run further test to check if this really was the problem, or my program called anything in this bpl I'll miss later on. But if you have any guesses, please share! (I don't really know much about this file at all...)