UPDATE: this issue has now been fixed in version 6.0.8.0 released on 19/11/2017.
If you use a password that contains symbols or signs, instead of just alphanumeric characters, you will find that the streaming API login does not work (nor does the Minimal Login option). It will fail with the message 'INVALID_USERNAME_OR_PASSWORD'.
So to use these features, please ensure that your Betfair password only contains alphanumeric characters, i.e. letters from the alphabet a-z, or A-Z, or numbers 0-9.
I don't have a list of which signs or symbols cause the problem, so you might find some symbols might work. To guarantee that it works, please don't use any symbols or signs.
Kind regards,
Gavin