Major problem with URLs

The site I’m linking to below was custom developed, and I really do not know where to begin to resolve the issue we’re having. The category/archives URLs are so bizarre; I don’t know how to describe them. Basically, we’ve run SEOMoz and found 1800 errors, namely with URLs like this:

http://www.overturemarketplace.com/category/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts/ask-the-experts?tid=obtn

As you can see, that is incredibly long. We don’t know why this is happening. There isn’t a way to get the URL that long just by clicking around, but the bots seem to find it. Every category is like that, too.

Any help you can provide would be greatly appreciated!