Password could not be changed because it is too short

If you are trying to change a user's password in the administration console and you get the error "The Main password could not be changed because it is too short" or "The WebMail password could not be changed because it is too short" then this either means that the password is too short (the minimum password length is set in Settings -> Security Settings -> "Minimum password length") or the password contains invalid characters.

Passwords can only contain non-space ASCII characters. So, if the password contains a space, or a non-ASCII character such as £, € or accented characters, then it will not be allowed. That is because email protocols such as POP3 do not allow that type of character in the password. (Spaces are used as separators, so cause ambiguity, and non-ASCII characters cannot be used because character encoding is not specified, so, for example, a £ could be encoded as a character 163 in ISO-8559-1 encoding, or characters 194, 163 in UTF-8 encoding, so it would cause unpredictable errors depending on what encoding method the email client software decided to arbitrarily use).