Can't see products after clicking category from front page after upgrade and plugins

[spawnie69]

I just started a new 1.58a zen store on 8.2.4 php, upgraded from 1.58 database along with the following plugins:

One Page Checkout
Ultimate URLS
Database backup
Square WebPay

Now I get the following internal server error when clicking the category to view an item.
It seems the dbase upgraded ok. I can see my categories and items within my admin.
Any advice?


Many thanks