Issue Magento Install in Plesk unable to add categories

[Trevor Towler]

Hi, I have installed Magento onto on plesk. The website is not live yet as the domain is not currently pointing to the new site.

I have installed Magento and everything seems ok until I try and add categories, i get the error message
Class Magento\CatalogInventory\Api\Data\StockItemInterfaceFactory does not exist

Has anyone else encountered anything similar?