One of the systems we use here has two slightly different front ends (same everything apart from the final presentation - windows or terminal based). They have differing password requirements. e.g. one accepts spaces in the password, the other will tell you that you entered the wrong password. All standard printable characters in the target region should be a minimum for passwords, or at least those accessible from the keyboard. Then again, is a space a printable character since it doesn't actually print anything? :-O