Hi,
This error indicates that the page is trying to load too much data from the database.
I suppose that you must have changed the number of elements listed by default on the listing.
For each cart / wishlist, HikaShop has to load the full cart/wishlist (all the products, the prices, the discounts, the addresses, the shipping methods, the payment methods, etc. With 20 carts, which is the default number of elements displayed per page, it works fine.
But for 500 carts (or another big number) to be loaded on the same page, that's bound to have the page crash.
So I would recommend to check on that.
Unfortunately, there is not much we can do to avoid this.