When doing tech support, it's very common to not be able to reproduce the problem being reported. Frequently, the reason you can't reproduce the problem is that it doesn't exist (and I've already mentioned how long it can take to debug a problem that doesn't exist). When you're on the phone with someone discussing their problem, it's considered impolite to tell them "You fatted-fingered f*ck, pack up your computer, send it back to the factory and resume grooming your mate." Instead tech support folks composed the following phrase for their logs "error disappeared upon testing."
Today, I was performing a routine apache configuration modification. I had to set up a virtual host with a CGI script alias. This is a very, very routine task and should have taken five minutes to do. Because I refuse to commit the syntax to memory, much of that five minutes involves looking for the right book (for me, that is Apache Server Administrator's Hanbook). In any case, I spent close on an hour trying to get this to work. The virtual host indeed was working, but the script alias was executing the CGI program. I was utterly confused, dejected and morose.
Then I remembered that the apache server I built didn't have the CGI module compiled into it. It could never do what I asked it to do. The solution was to build another server with the CGI module and configure to taste.
And the error disappeared upon further testing.
So, I've begun packing up my computers to send back to the factory. Should you need me, I'll be out looking for a comfortable tree to swing from with my fat fingers.