g1smd - 10:28 pm on Nov 21, 2012 (gmt 0)

Add a blank line after each RewriteRule for human readability.

Get the DirectoryIndex and Options lines up to the top.

Change your non-www/www redirect to this:
RewriteCond %{HTTP_HOST} !^(www\.example\.com)?$
RewriteRule (.*) http://www.example.com/$1 [R=301,L]

Add an extra RewriteCond condition in the ruleset that internally rewrites.
This will test that REQUEST_URI is NOT ^/customerrors/