Interestingly, this is the response from the web server when Chrome requests the file:
HTTP/1.1 304 Not Modified
Date Thu, 01 Aug 2013 17:13:01 GMT
Server Apache
Connection close
ETag "5a149e9-402-4e2e5ccdd308a"
The server is in a different time zone. The server and client clocks are correct.
I last updated the file at 19:12 GMT+2 (which FTP shows correctly as the timezone adjusted modification time)
When I ran this it was 19:15 in Gibraltar, which was 18:15 in UK, which in summer is 17:15 GMT or UTC.
This was the request:
GET /bingo/offline.appcache HTTP/1.1
Host test.nektan.com
Connection keep-alive
If-Modified-Since Thu, 01 Aug 2013 17:01:59 GMT
If-None-Match "5a149e9-402-4e2e5ccdd308a"
User-Agent Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.95 Safari/537.36
Accept-Encoding gzip,deflate,sdch
Accept-Language en-US,en;q=0.8
The crux is that apache is returning the 403 response incorrectly for a file which was just modified. This would appear to be a bug in Apache (which is unlikely) or other time zone related issue?