error on register.php page

I have installed the avatar hack that allows members to select an avatar from a drop down menu when they register. Since doing so I get the following error:

An error has occured on the script of this page.

line: 680
char: 5
error: 'document.forms.0.avatersel.selectedIndex' is null or not an object
code: 0

I haven't noticed any problems registering but don't like seeing errors in a page. I know for a fact that the error is being caused by the avatar hack.

Anyone know how to eliminate the error I am getting on the registration page?

Thanks in advance for any help offered.