My b2evolution Version: 2.4.2

Hi, I'm receiving an error when clicking 'save' on my wife's blog. I just installed it a few days ago and it worked fine for like 3 days. This morning it started producing the following error:

Fatal error: Call to a member function on a non-object in /home/3281/domains/modbewomensmodernmodestclothing.com/html/inc/items/model/_itemlight.class.php on line 213

Ok, here's the thing, it takes the user to the error page, but I found out that all the 'test' postings I sent were posted on the blog, so it's still posting them, it just dead ends at the error page.

I replied with a question in another thread and was asked to start a new thread.

EdB wrote:

Oh and some helpful information will be stuff like what version of b2evolution you're running,

Version 2.4.2

EdB wrote:

have you had this problem since immediately right away or did it start after some sort of change you made?

No, it worked fine for a few days. I didn't change anything immediately prior to this problem.

EdB wrote:

Did you change skins or add plugins or do any creative editing on any files?

I'm trying to learn about the coding etc, so I was playing around with different features, but I only messed within the guidelines in the notes on the pages, and I didn't do anything as far as function, just visual effects so far as I know.

EdB wrote:

Also what kind of server your host is (windows or something reliable),

I'm not sure the answer to this question.

EdB wrote:

and maybe stuff like php version on your server too.

MySQL 4.1.11

EdB wrote:

By the way a link to your blog will probably be way helpful too.

http://modbewomensmodernmodestclothing.com

This is what is at the error line:
case 'chapters':
$permalink = url_add_tail( $blogurl, '/'.$this->main_Chapter->get_url_path().$urltail );
break;

Thanks in advance for your time!

Josh