The Perfect Job - error when clicking for job details

http://www.devshed.com/Server_Side/MySQL/PerfectJob/PerfectJob1/page1.html

The Perfect Job (part 1) was written in June 28, 2001 and I have a problem with it. After having spent quite some time searching for the original discussion threads on it I conclude they don't exist anymore.

You guys are very clever and I've found hundreds of answers on this site, but this one eludes me.

When I click on a job (ie 'Senior Web Developer (X5436)') within the job_list.php page I've set up I get sent to the error page which I believe is defined by the code at the top of the page it's trying to interact with (job_details.php):


// check for missing parameters
if (!$jcode || $jcode == "")
{
header("Location:error.php");
exit;
}


Because when I alter that bit of code to point to errorsplurg.php it does indeed try to send me to errorsplurg.php.

When I hover over the link on job_list.php I see that it is linking correctly to job_details.php?jcode=X5436

So why is it that job_details.php isn't accepting that jcode exists?

Do I need to add more detail, or have I made it clear?
Thankyou for reading this, much loving, Chris