Every 5 to 10 mins when you click on a catergory or main page it will display the header bar and categorys down the side but the main page will just remain white.

Sometimes it says "There are no products in this category" or something like that even though there could be 500 odds ??????. If you click the category again they will then appear?

This isnt too good if someone comes to your site and checks the category the are interested in and it says there are none???? when you do have the stuff they need.

Any ideas why this happens and how to mend it?