The errors you see in your awstats may not be actual errors at all. If I were to visit your website and miss typed the URL that would generate a error because the page was not found. but in all actuality that page never existed.
for example, I want to visit this page
http://www.yourwebsite.com/pages/storepolicies.php but I typed in http://www.yourwebsite.com/pages/mtorepolicies.php (I miss spelled storepolices) this would generate a error but the error was from the visitor, not because there was something wrong with my website.
If you delete a image from your website but it is still listed on some of your pages you will receive errors also because the image couldn't be displayed.