404 error codes

I have been getting a lot of 404 error codes lately, primarily from the two URL's shown below. Anyone know why they have shown up and how to get rid of them?

Required but not found URLs (HTTP code 404)
URL
/catalog/manufacturer.asp
/images/spacer.gif

ERROR HITS REFERERS
http://www.theoutdoorsportsshop.com/firearms.htm
http://www.theoutdoorsportsshop.com/firearms.htm

I don't see the problem. You must have fixed it.