Normal cause of that problem -- the CGI exists in more than one location, and you only updated one copy. The 'problem' user is looking at the other copy.

CGIs should only be cached if they're using GET -- POST is considered an 'unsafe' operation, which must be reapplied, but it's possible that a proxy might cache the results from a GET request, and it really can't tell the different between a CGI and a static page. (it can guess, but it's only a guess)

Depending on how much traffic you get, I'd probably either just tail the access log, grepping for the user's IP address, and see if they make contact with your machine (and what the file is they're asking for). If they don't, I'd check their proxy settings, and see if they're routing their traffic through some other host.

After that, you start getting into the trickier situations -- do they have your server overridden in their /etc/hosts or the equivalent (yes, it seems strange, but I've been known to have some machines send all requests for the production server to the development server, so I don't have to worry about absolute URLs). Is DNS working for the user? Are the using the correct DNS server? (seems like a stupid question -- until we found that somehow AOL had found a development DNS server that the admin hadn't put on a closed subnet ... lost ~2 weeks of my time on that one)

Is there anything else different about the user? Different browser? different browser version? different OS? something? Find out what that is, and you might have some insight into the problem.

Oh ... and if you're concerned about caching ... look into cache control headers.

Update: this is a really stupid thing, but I just remembered -- back in 1994?5? or so (back in the days of Netscape 0.9), we had some massive issues when daylight savings first rolled around -- caching got all messed up, as the browser was sending the wrong timestamp to the server, and the server would respond with 304. I would hope there aren't any browsers/servers/proxies that still have this problem, but when it happens, it's really annoying. If the user's stuff suddenly works after the change has been in for an hour, it's something to look at.

If it is in fact a problem with a cached page generated by a CGI script, the user should be able to fix the problem by clearing their cache, quitting their browser, then re-visiting the page; or by force-reloading the page in their browser (Shift-Reload in Mozilla/Firefox/Netscape, either Ctrl- or Shift-F5 in IE).

Thanks to all :)

I thought it might be something to do with the browser caching the script. But as pointed out by sgifford, the browser only caches the result.

So it's probably the script. I did more testing but couldn't nail down the bug. Basically it's to do with the value of a variable that is inserted or updated into the database. This value should not exceed a certain upper bound. But for this user, it had exceeded that maximum value.