I have two web sites on a MOSS farm.  The first is reserved for authors and the second one is exposed to the internet allowing anonymous access.  Recently, we receive intermitten 403 errors (Event ID 1314) when a user tries to access a certain page.  This only occurs on the author site.  After some searching, I found references to this error in these threads (objectmix, microsoft)

Basically, there are two workarounds for this problem:

1. Set <identity impersonate="false" /> in the web.config file.  I actually did this in the public web application, so that's why we never saw this error on the public web site.
2. Give users access to the web site's bin folder. 

I went with the second workaround.  In addition to the bin folder, I also needed to give users access to the App_Data folder. 

Filemon.exe rocks!  It showed me exactly what I needed to know to fix this problem: the path and user name which is getting the access denied error.