I am new with CMSMS but I can all ready say I love it

Still I have this one problem, I am planning to change one of my sites to CMSMS, but I have many users, who are using scandinavian letters in login name, like ä, Ä, ö, Ö and so on, when I installed CMSMS everything went just great, but when I try to add users with login name of scandinavian letters, I allways get error: "Error in user name, wrong characters" (this is my own bad translation because error is in Finnish

Thank for advance
tapiol