Web Server, http Status codes

This is a chart for http status codes returned from the server hosting interfacebus.com for the month of July. There are a dozen or so pages that have been orphaned and moved to a new page address; however, those old addresses still get traffic [code 301]. The 'Document Not Found' or 404 code normally comes from people linking in or typing in the wrong page address. I try to catch some of that missed traffic by generating a page with the incorrect address ~ if it's getting traffic. Many mis-spelling can't be corrected, as they are missing the ".html" at the end of the address. There are 115 pages that target bad page addresses....

The server issues, codes 404 and 500, are just that ~ problems with the web server. Not sure what code 405 is?