Sorry, the $User['nopost'] I mentioned above was, I beleive, a red herring. If you ignore that part the rest of what I've said should make more sense. The editproduct.php file is called with the following 3 URLs depending of whether you are editing, marking as sold, or relisting a product... http://www.mkivsupra.net/pp-classifi...php?phoedit=18 http://www.mkivsupra.net/pp-classifi...ct.php?sold=18 http://www.mkivsupra.net/pp-classifi....php?resell=18
$ueditpho is then set using intval($phoedit) regardless of which parameter is actually being used to pass in the product ID. So for editing it worked, but the SOLD IT! and RELIST IT! options didn't work. To further prove this was the problem, the URL that the user was then redirected to after the error message was... http://www.mkivsupra.net/pp-classifi....php?product=0
...which just displays a blank page because the product is zero. It was actually this that pointed me in the direction of where the problem may lie.
I can revert this file back if you would like to see for yourself?