Re: When logged in to BuddyPress.org some links do not work?
You should ask this question as well in the WPMU forums as it is the WPMU registration functions that allow usernames to be created with a space in them and it is the authentication functions (when a user logs in) that then has an issue with the space.
I do not know if this has already been addressed in a newer version of WPMU, but Andy is aware of this issue and I assume that he has communicated it to Donncha.
You are limited in what you can do, but deleting the username is not advisable.
You could manually edit each user account that has this issue. If you do so, you’ll of course first want to make sure you have a backup of your database. But, if you go this route, you’ll need to tell each of those affected users that you have changed their login credentials. Otherwise, they will not be able to log in.
As far as changing the display name, that will have no affect on the username. Those are two different pieces of data.