During upgrades for a website a was googling after an error.
I thought I will find the solution, like 10 stackoverflow links... No, I found more than 65.000 broken pages which include that error. Go people -> Check your store ! Maybe you have some broken pages out there.
What causes the error?
I called the id of a product directly and that is not allowed anymore.
change this to:
Having problems upgrading your webshop ? Just write me a message