Problem with the inventory function

[beachhouse]

When I go into the manager and try to access the inventory , the screen pops up blank. I have found if I click on work sheet and then close the work sheet then i am able to see the inventory numbers. Why is this happening?

Also, when the inventory numbers pop up sometimes in the "+/-" column there are already numbers and sometimes there are zeroes. Is there a way to have it always pop up with zeroes so I can easily adjust me inventory?

Thanks