Thanks for making the change. I did not expect that change to fix the problem based on your previous comment. I just needed that line removed so I could track down the real problem.
If you do a "View Source" on your home page you will notice the following:
<div class="tabs_vertical_frame"><span class="bg_top"></span></p>
You will notice in the code above that you have a terminating html paragraph but not an opening html paragraph. Also, the terminating html paragraph is being rendered in the middle of the tabs_vertical_container class.
1) You have an un-terminated paragraph in your home page text
2) You have an un-terminated paragraph in your vertical tabs title
3) You have a plug-in loaded that contains or is configured to contain text with an un-terminated paragraph
Take a look and see if you can trace it down. If you cannot find an unterminated paragraph try wrapping the vertical tabs shortcode with the raw shortcode ([raw] [/raw]). This could be a conflict with the WordPress auto-paragraph functionality.
Let me know.