There's a bug in line 18 of templates\Traq2\roadmap.php, it's:
and the bug is that the anchor is created in the form of 'milestone-'.$milestone['milestone'] and it should be 'milestone-'.$milestone['slug']
Also there's no error if I go to a nonexistent milestone like milestone-qwerty, it's just an empty milestone page.
Thanks for reporting this. I've gone ahead and fixed this.