sass, the problem could be any number of things, really. Are you "attaching" the file to the email, or are you opening the HTML file and using copy/paste?
Your email program may be modifying the contents before it is sent. Your ISP may be modifying the email before it leaves your email server. The recipient's mail server may be modifying the email when it arrives. The recipient's email program may be modifying it or displaying it incorrectly.
If some recipients can view it and some cannot, the problem lies most likely on the other end. Probably lies in whatever the recipients are using to view the email (is it a program on their PC, like Outlook or Outlook Express or Thunderbird, or is it web based email?). But with all of the spam and spam filters, their ISP could certainly be guilty of modifying the email before they receive it.
If you want, send the email to support@thetournamentdirector.net and I'll look at it.