Yes, I can confirm this error occurs for me too.
Unfortunately, the error messages in the JavaScript console are not very informative.
I suspect what might be happening is that the URL generated by selecting so many different zoos to search across - is too long and thus generating an error in the browser?
It certainly doesn't cause an error if you select fewer zoos - I tried selecting every zoo in the US and then a dozen from Canada and it was fine. It was only when I selected all the zoos in Canada as well that it caused the error - so it's likely the threshold is somewhere between those two figures.
It's a pity that the system is not intelligent enough to allow you to select just "United States" and "Canada" and search all zoos contained within those two categories.