To Avatar T-Man:
Solution found.
What was causing it might interest you.
Two parameters must be put together: player must have an Azerty keyboard (like the ones we have in France) and player must have a password with numbers in it.
In the logging screen when pressing Metaverse button, some characters are not accepted, while others are assimilated ; for instance, pressing "1" or "MAJ + 1" still displays "1" as a result. In Azerty keyboards, by default, you must press MAJ+1 to display character "1" ; in Qwerty keyboards this is the opposite. So even if I was comforted that MAJ+1 or 1 did display the number "1" in the form field, I continued pressing the usual keys.
In GalCiv2 this didn't cause many problems, except this one: in the nickname part of the logging form I can press 1 or MAJ+1 and this displays 1. So I supposed that in the password part (remember we cannot read what is typed in password field), this was the same. But it wasn't. In the password field, pressing MAJ+1 with an Azerty keyboard translates the character in another way than in the nickname field, and doesn't translate it to the number "1". That is the reason why my password, which has numbers in it, was never typed the right way.
Though the problem does sound silly, I had no way to guess it since in the "logging" field of the form characters and numbers are displayed the right way, whether you use the Qwerty-american way of entering numbers or the Azerty-french one.
Maybe would it help some other french or european player !