Rogue Error Message appears

Having aborted an upgrade from 1.5.6.4 to 3.0.2 due to errors I managed to restore the older version (1.5.6.4) and get it working - or so I thought.

Prior to attempting the upgrade (using the download and instructions obtained from the Opencart web site) version 1.5.6.4 had been working correctly, including the ability to create and edit entries for catalogue items. So the issue is clearly not an inherent bug but can, I believe, be entirely attributed to the upgrade process throwing up errors instead of completing smoothly and leaving corruption in its wake.

Currently, when in the admin processes and selecting Catalog > Products and then attempting to edit any of the entries the multi-tab page initially comes into view but is then, as soon as the browser finishes presenting the page, split by an additional section containing the "The page you are looking for could not be found! Please contact your administrator if the problem persists." message.

The multi-tab product page tabs are still showing at the top and each tab is selectable.

Below this is the error seemingly emanating from Home > Page Not Found! and having the appearance of a page inserted as evidenced by this section ending with an instance of the Opencart standard page footer. Examination of the source code of the delivered page indicates that an extra container div has been inserted.

Below that content of the selected tab for the product appears together with another instance of the Opencart standard footer.

Examination of both the Opencart logs and those provided by the hosting company do not show any entry relating to a failure to find a page in the Opencart system.

Despite this interjection of the 'page not found error' section, the editing facility otherwise works as it should and the content of the relevant entry can be edited and the amendments saved as one would expect.

Something has gone amiss and is causing the seemingly rogue appearance of an error message. But what?

Attached PDF gives an example of how the page ends up in the browser. Incidentally, I have tried this in two different browsers with the same results so it does not seem to be a browser issue. In case it helps I have also attached the source code of the same page.

Thanks, John

Source file didn't upload first time.

Caused by an installed extension. Also check your page permissions. Check error / server access logs. Forum rules.