Strange, I'm not getting this issue.

Does it happen for all pages on the wiki, or only certain ones?

If you log out and back in, does that fix it?

I just tested it and you can't view the wiki if your name begins or ends with an underscore. Dashes are fine though. Underscores are also fine in the middle.

I might look into it later, but no guarantees ... sorry about that. I haven't looked into the wiki authentication before. I don't know how easy it would be to fix.

Consider changing your username.