The § is not ascii. How did you set your password?
PuTTY also (correctly) uses UTF-8 encoding for passwords. So either your server indeed does not use UTF-8; or you have used a broken SSH client (not supporting UTF-8) to set your password.
You're right, § is not ascii.
I did not set the password. The password was set by the the client, I work for. I will inform him about the issue and ask to change it.
Thanks for your fast response!