Mailchimp HTML coding problem

Hi there,

Yesterday I sent out the April newsletter for the non-profit organisation I work for using Mailchimp.

The format of the newsletter was fine when viewed from an email inbox but when you click to view it in your browser, the online/archived version formatting was all over the place.

You can view it here:
http://eepurl.com/kyNCz

I emailed Mailchimp and this was their response:

"Many email clients use more relaxed standard for rendering HTML. However, we recently upgraded the archive page to use stricter HTML rendering standards. This improves the quality and consistency of the emails, plus follows guidelines for best practices for display HTML on the Web.

Because of the tighter standards on the archive page, any HTML which is not valid will not render as expected. This can include issues with improperly set up tables or unclosed elements."

I am not experienced with HTML coding. Would you be able to take a look at it and show me where the coding went wrong and how  I can fix it?

Thanks,

Samantha