What do these website owner resources mistakes mean?
 

A little over a month ago the company I worked at launched a new site. The site was down for a weekend and ever since I have been getting a ton of errors.
1. Over 500 access denied errors. We have our robots.txt setup properly, so what are these from?
2. I am showing 125,000 not found errors and it keeps increasing. The site has less than 20000 pages so where are these other things from?
3. Over 20 400 response code errors. The only pattern I have noticed with these are they all have a % in the title.
4. Under Index Status the total amount has dropped about 20% since the site launched.
5. My sitemap submission had maxed out at about 50% indexed and has been dropping since. My guess is that since some of the new stuff has redirects from older sites and it is showing up as duplicate content.