Hi Colin! Sorry about the 404.
It was the View Report Card link, correct? (The badge image itself doesn't have a link.) This is a known issue, effects all "You earned ..." emails, and was a bit lower priority initially, although that's been bumped up as there are a fair number of reports about this. (A template at the bottom is broken as well; I believe this currently affects all email.)
As a workaround, to access your Report Card, use the drop-down menu at the upper-right of your Code School account, and choose the Report Card option.
I've added your report to the issue.
Thanks for reporting this!