Just upgraded a Magento installation from 1.6.1 to 1.2.1 and ran into some minor issues with file not found error like the following:
Warning: include(Mage/Adminhtml/Model/System/Config/Backend/Catalog/Inventory/Managestock.php) [function.include]: failed to open stream: No such file or directory in /home/noblesg/public_html/shop/app/code/core/Mage/Core/functions.php on line 73
After some research on Magento forum…found a solution. It appears to be a common issue with version 1.2.1, the fix for this is fairly simple, just copy the files from:
if you look carefully the url path will correspond to your file structure in Magento, just copy the files that you are missing by traversing the folder and right-click the file and choose “Save As” and save the file(s) back into your magento folder and you should be ready to go.
For me, I had to recreate the “Catalog” folder and all files within underneath /config/backend/ and also the “Search” folder and all files within underneath Adminhtml/Model/System/Config/Source/Catalog/ to fix the “Catalog” and “Inventory” links in the admin page.