Script Error! Please Help!

On the site bidbuybay(dot)com

There is an issue with registering.

We are getting a error everytime there is a sign-up.

Any ideas?

Willing to make an offer to whoever thinks they can fix.

Error
Error: The requested address '500.shtml' was not found on this server.

Thanks

I just registered and didn't see an error, you get it all resolved?