[Tom Bunch]

I'd speculate that there's probably some syntactically important HTML character that needs to be escaped or balanced, but if you're unable to find the issue I think you're going to need to zip up your report template and mail it to the helpful humans at omniplan@omnigroup.com.

Steps for doing so:

• From OmniPlan's Help menu, select "Send Feedback…"
  If prompted you need not include a file.
• Now open up OmniPlan -> Preferences and go to the HTML tab
• Select your template
• Use the context menu (right click or click the gear button) to "Reveal in Finder"
• Drag the whole folder into the mail message
• Include a brief description of the issue

-Tom