OK I have my fingers crossed on the following fixes. I had to copy the source code for your page out and then do validations and fixes from within my XHTML editing program. With the following, supposedly you will be down to only 1 error, and that is a piddly little thing you can do nothing about. I've had to modify a few things a little from your original code, and there were stray tr and td tags getting inserted that I have no idea where they came from (hopefully they weren't inserted by the theme itself). After you make the following corrections, we shall see. (I recreated all your text widgets in one of my test blogs and with the following, things work fine and only came up with that one odd error we aren't going to worry about.
For AO! Message boards text widget replace the code you have with this.
<p><a href="http://absoluteomnibus.freeforums.org/" target="blank"><img title="authority1" src="http://absoluteandomnibus.files.wordpress.com/2010/12/aoforumlogo1.png" alt="" width="200" height="100" /></a></p><p><a href="http://absoluteomnibus.freeforums.org/" target="blank">Chat it up in the AO! Forums!</a></p>
In the C2E2 text widget, delete everything in that widget and put the following
<p><a href="http://www.c2e2.com/" target="_blank"><img width="200" height="400" title="C2E2" src="http://absoluteandomnibus.files.wordpress.com/2010/12/c2e2_2011_200x400.gif"></a></p>
In the Con List From text widget delete everything and replace with this
<p><a href="http://firstaidcomics.wordpress.com/shows/" target="_blank"><img width="200" height="100" title="Weekly New Releases" src="http://absoluteandomnibus.files.wordpress.com/2010/12/firstaid200x100.png"></a></p>