A PRE is a Page Request Error. That is what happens when you have too many things running at once. It is because there are too many page requests to MTurk at once. You are only allowed a certain amount, maybe 2 every second. SO if you have a Panda refreshing the page at the same time you are submitting (which sends a request to the page) they will run into each other. The best way to avoid them is to stagger your Page Requests or turn off scripts that cause Page Requests. If you want to catch a fast batch like Zoltar, only have one or two fast Pandas for Zoltar and turn off your HitScraper or HitFinder and HitMonitor. Otherwise put your Pandas at longer intervals.