I would check each criteria carefully,
First I would remove all except Stock, then if that returned data, I would include Date, after running that ensuring that data was returned I would include Low (repeat process) and finally High.
When the query stops returning data you should look into why it's stopped. Perhaps it's the date portion. IE if the date on Table Prices is '2010-02-05 12:35:17' it won't match '2010-02-05'
Maybe Stock isn't set to 'XXX'
Please test these and post more information if the issue persists.