Chris's Compliance Madness Thread

I'm not sure if this belongs in coding discussion, so apologies in advance if there's a more suitable place for it.

Recently, since I suffer from vB mod-itis, I've started going through every template to try and get my site to score better on WC3's compliance checker.

Here's a few snippets that failed, and I'm hoping someone can tell me what I'm doing wrong, or if WC3 is just being nuts.

<a href="http://www.sevenstring.org/forum/showthread.php?t=375"><span 
class="portalblue">Ben Carroll / Ra</a></span><br />

The error here is "end tag for "span" omitted, but OMITTAG NO was specified."

I've no idea what OMITTAG NO is, but I haven't specified it anywhere. I get that on every line of the "Reviews and Interviews" CMPS block on the front page of my site. The closing bracket for the /a directly after the word "Ra" in this case is highligted red.

What am I not doing correctly in that line of code above?

[high]* Guest210212002 goes off to google OMITTAG[/high]