> I am trying to figure out exactly what causes 
> the 'file has moved from URLa to URLb' or 'file has 
> temporarily moved' error message.

> How does the server know I am using an offline 
> browser?
Either using the Browser ID sent, or by detecting the 
robots.txt request, or by detecting the number of 
simultaneous requests, or by detecting that all links 
in a page are being tracked one by one. 

You can not avoid offline browser detectors, but there 
are simpler ways to avoid offline browsers (see at 
<http://www.httrack.com/HelpHtml/abuse.html#WEBMASTERS>)

Generally, 'moved pages' are mistyped link, such as:
<http://www.foo.com/bar> instead of 
<http://www.foo.com/bar/>
(ending / missing)
Or <http://www.foo.com/Bar/> instead of 
<http://www.foo.com/bar/>
(case mismatch)

The default behaviour is to download only pages in 
current directory/location (plus some images and other 
related files), therefore moving from 
<http://www.foo.com/Bar/> to <http://www.foo.com/bar/> may 
cause the link to be considered as 'external'.