Problems with german Umlaut (Ä, Ö, Ü)

[Redbeard]

Hello.
I'm new to PrestaShop and so far I am very impressed by it. But now I've come to a problem I just cannot solve.

When somebody registers with a name containing a German Umlaut (Jörg Müller) everything is fine until he (or she) is pressing "Send order". The he gets a Sricpt Error 500.

What can be the reason for this problem? Any idea would be highly appreciated!

Thanks,
Red

P.S.
I found out that this could be a problem with the BankWire module. The file I'm getting this error in is validation.php